0000078713 2021-05-01 2021-05-01 0000078713 pstx:S000003991Member 2021-05-01 2021-05-01 497 2020-12-31 0000078713 false N-1A 2021-07-09 2021-07-09 <div style="line-height:13.02pt;margin-top:12.84pt;text-align:center"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 11.16pt; letter-spacing: 0px; top: 0px;display:inline;"><div style="font-weight:bold;display:inline;">Pioneer Fund</div></div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 11.16pt; letter-spacing: 0px; top: 0px;display:inline;"><div style="font-weight:bold;display:inline;"> </div></div></div> <div style="line-height:11.16pt;margin-top:9.98pt;text-align:center"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;"><div style="font-weight:bold;display:inline;">Supplement to the Prospectus dated May 1, 2021 (as revised June 9, 2021)</div></div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:9.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;"><div style="font-weight:bold;display:inline;">Principal investment strategies</div></div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:3.0pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The following replaces the corresponding information under the heading </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">“</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">Principal investment strategies</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">”</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;"> in the section entitled </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">“</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">Fund summary</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">”</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">:</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund invests in a broad group of carefully selected securities that the </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">fund's adviser believes are reasonably priced, rather than in securities </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">whose prices reflect a premium resulting from their current market popularity. </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">The fund invests predominantly in equity securities. For purposes of the </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">fund's investment policies, equity securities include common stocks and </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">other equity instruments, such as securities of other investment companies </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">(including mutual funds, exchange-traded funds and closed-end funds) that </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">invest primarily in equity securities, equity interests in real estate investment </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">trusts (REITs), depositary receipts, warrants, rights and preferred stocks.</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund primarily invests in securities of U.S. issuers. The fund may invest </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">up to 15% of its total assets in securities of non-U.S. issuers. The fund will </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">not invest more than 5% of its total assets in the securities of emerging </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">markets issuers.</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund may invest up to 15% of its net assets in REITs.</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund may invest in initial public offerings of equity securities. The fund </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">may also invest in investment grade and below investment grade debt </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">securities (known as </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">“</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">junk bonds</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">”</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">).</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund may, but is not required to, use derivatives. The fund may use </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">derivatives, such as stock index futures and options, for a variety of purposes, </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">including: in an attempt to hedge against adverse changes in the market </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">price of securities, interest rates or currency exchange rates; as a substitute </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">for purchasing or selling securities; to attempt to increase the fund's return </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">as a non-hedging strategy that may be considered speculative; to manage </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">portfolio characteristics; and as a cash flow management technique. The </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">fund may choose not to make use of derivatives for a variety of reasons, </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">and any use may be limited by applicable law and regulations. The fund </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">may also hold cash or other short-term investments.</div></div> <div style="line-height:11.16pt;margin-left:0%;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund's investment adviser uses a value approach to select the fund's </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">investments to buy and sell. Using this investment style and environmental, </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">social and corporate governance (ESG) analysis described below, the adviser </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">seeks securities selling at reasonable prices or substantial discounts to </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">their underlying values and then holds these securities until the market </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">values reflect their intrinsic values. The adviser evaluates a security's </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">potential value, including the attractiveness of its market valuation, based </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">on the company's assets and prospects for earnings growth. In making that </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">assessment, the adviser employs fundamental research and an evaluation </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">of the issuer based on its financial statements and operations. In selecting </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">securities, the adviser considers a security's potential to provide a reasonable </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">amount of income. The adviser focuses on the quality and price of </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">individual issuers.</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The adviser integrates ESG analysis into its investment process by focusing </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">on companies with sustainable business models and evaluating ESG-related </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">risks as part of its research recommendations. In addition, the adviser </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">generally excludes corporate issuers that do not meet or exceed minimum </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">ESG standards, based on a system that uses ESG ratings provided by third </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">parties or internal sources. When using ESG ratings to exclude corporate </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">issuers and evaluating ESG issues generally, the adviser considers ratings </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">in the context of an issuer’s respective sector or industry. The fund generally </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">will not invest in companies significantly involved in certain business activities, </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">including but not limited to, the production of alcohol, tobacco products </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">and certain controversial military weapons, and the operation of thermal </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">coal mines and gambling casinos and other gaming businesses.</div></div> <div style="line-height:13.02pt;margin-top:12.84pt;text-align:center"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 11.16pt; letter-spacing: 0px; top: 0px;display:inline;"><div style="font-weight:bold;display:inline;">Pioneer Fund</div></div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 11.16pt; letter-spacing: 0px; top: 0px;display:inline;"><div style="font-weight:bold;display:inline;"> </div></div></div> <div style="line-height:11.16pt;margin-top:9.98pt;text-align:center"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;"><div style="font-weight:bold;display:inline;">Supplement to the Prospectus dated May 1, 2021 (as revised June 9, 2021)</div></div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:9.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;"><div style="font-weight:bold;display:inline;">Principal investment strategies</div></div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:3.0pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The following replaces the corresponding information under the heading </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">“</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">Principal investment strategies</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">”</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;"> in the section entitled </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">“</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">Fund summary</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">”</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">:</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund invests in a broad group of carefully selected securities that the </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">fund's adviser believes are reasonably priced, rather than in securities </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">whose prices reflect a premium resulting from their current market popularity. </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">The fund invests predominantly in equity securities. For purposes of the </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">fund's investment policies, equity securities include common stocks and </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">other equity instruments, such as securities of other investment companies </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">(including mutual funds, exchange-traded funds and closed-end funds) that </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">invest primarily in equity securities, equity interests in real estate investment </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">trusts (REITs), depositary receipts, warrants, rights and preferred stocks.</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund primarily invests in securities of U.S. issuers. The fund may invest </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">up to 15% of its total assets in securities of non-U.S. issuers. The fund will </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">not invest more than 5% of its total assets in the securities of emerging </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">markets issuers.</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund may invest up to 15% of its net assets in REITs.</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund may invest in initial public offerings of equity securities. The fund </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">may also invest in investment grade and below investment grade debt </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">securities (known as </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">“</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">junk bonds</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">”</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">).</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund may, but is not required to, use derivatives. The fund may use </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">derivatives, such as stock index futures and options, for a variety of purposes, </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">including: in an attempt to hedge against adverse changes in the market </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">price of securities, interest rates or currency exchange rates; as a substitute </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">for purchasing or selling securities; to attempt to increase the fund's return </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">as a non-hedging strategy that may be considered speculative; to manage </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">portfolio characteristics; and as a cash flow management technique. The </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">fund may choose not to make use of derivatives for a variety of reasons, </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">and any use may be limited by applicable law and regulations. The fund </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">may also hold cash or other short-term investments.</div></div> <div style="line-height:11.16pt;margin-left:0%;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund's investment adviser uses a value approach to select the fund's </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">investments to buy and sell. Using this investment style and environmental, </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">social and corporate governance (ESG) analysis described below, the adviser </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">seeks securities selling at reasonable prices or substantial discounts to </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">their underlying values and then holds these securities until the market </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">values reflect their intrinsic values. The adviser evaluates a security's </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">potential value, including the attractiveness of its market valuation, based </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">on the company's assets and prospects for earnings growth. In making that </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">assessment, the adviser employs fundamental research and an evaluation </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">of the issuer based on its financial statements and operations. In selecting </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">securities, the adviser considers a security's potential to provide a reasonable </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">amount of income. The adviser focuses on the quality and price of </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">individual issuers.</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The adviser integrates ESG analysis into its investment process by focusing </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">on companies with sustainable business models and evaluating ESG-related </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">risks as part of its research recommendations. In addition, the adviser </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">generally excludes corporate issuers that do not meet or exceed minimum </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">ESG standards, based on a system that uses ESG ratings provided by third </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">parties or internal sources. When using ESG ratings to exclude corporate </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">issuers and evaluating ESG issues generally, the adviser considers ratings </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">in the context of an issuer’s respective sector or industry. The fund generally </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">will not invest in companies significantly involved in certain business activities, </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">including but not limited to, the production of alcohol, tobacco products </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">and certain controversial military weapons, and the operation of thermal </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">coal mines and gambling casinos and other gaming businesses.</div></div> Pioneer Fund 2021-05-01 Principal investment strategies <div style="line-height:11.16pt;margin-left:0%;margin-top:3.0pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The following replaces the corresponding information under the heading </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">“</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">Principal investment strategies</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">”</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;"> in the section entitled </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">“</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">Fund summary</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">”</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">:</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund invests in a broad group of carefully selected securities that the </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">fund's adviser believes are reasonably priced, rather than in securities </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">whose prices reflect a premium resulting from their current market popularity. </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">The fund invests predominantly in equity securities. For purposes of the </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">fund's investment policies, equity securities include common stocks and </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">other equity instruments, such as securities of other investment companies </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">(including mutual funds, exchange-traded funds and closed-end funds) that </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">invest primarily in equity securities, equity interests in real estate investment </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">trusts (REITs), depositary receipts, warrants, rights and preferred stocks.</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund primarily invests in securities of U.S. issuers. The fund may invest </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">up to 15% of its total assets in securities of non-U.S. issuers. The fund will </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">not invest more than 5% of its total assets in the securities of emerging </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">markets issuers.</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund may invest up to 15% of its net assets in REITs.</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund may invest in initial public offerings of equity securities. The fund </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">may also invest in investment grade and below investment grade debt </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">securities (known as </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">“</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">junk bonds</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">”</div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">).</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund may, but is not required to, use derivatives. The fund may use </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">derivatives, such as stock index futures and options, for a variety of purposes, </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">including: in an attempt to hedge against adverse changes in the market </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">price of securities, interest rates or currency exchange rates; as a substitute </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">for purchasing or selling securities; to attempt to increase the fund's return </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">as a non-hedging strategy that may be considered speculative; to manage </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">portfolio characteristics; and as a cash flow management technique. The </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">fund may choose not to make use of derivatives for a variety of reasons, </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">and any use may be limited by applicable law and regulations. The fund </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">may also hold cash or other short-term investments.</div></div> <div style="line-height:11.16pt;margin-left:0%;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The fund's investment adviser uses a value approach to select the fund's </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">investments to buy and sell. Using this investment style and environmental, </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">social and corporate governance (ESG) analysis described below, the adviser </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">seeks securities selling at reasonable prices or substantial discounts to </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">their underlying values and then holds these securities until the market </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">values reflect their intrinsic values. The adviser evaluates a security's </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">potential value, including the attractiveness of its market valuation, based </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">on the company's assets and prospects for earnings growth. In making that </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">assessment, the adviser employs fundamental research and an evaluation </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">of the issuer based on its financial statements and operations. In selecting </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">securities, the adviser considers a security's potential to provide a reasonable </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">amount of income. The adviser focuses on the quality and price of </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">individual issuers.</div></div> <div style="line-height:11.16pt;margin-left:0%;margin-top:6.84pt;text-align:left"><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; margin-left: 0%; letter-spacing: 0px; top: 0px;display:inline;">The adviser integrates ESG analysis into its investment process by focusing </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">on companies with sustainable business models and evaluating ESG-related </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">risks as part of its research recommendations. In addition, the adviser </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">generally excludes corporate issuers that do not meet or exceed minimum </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">ESG standards, based on a system that uses ESG ratings provided by third </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">parties or internal sources. When using ESG ratings to exclude corporate </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">issuers and evaluating ESG issues generally, the adviser considers ratings </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">in the context of an issuer’s respective sector or industry. The fund generally </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">will not invest in companies significantly involved in certain business activities, </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">including but not limited to, the production of alcohol, tobacco products </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">and certain controversial military weapons, and the operation of thermal </div><div style="color: rgb(0, 0, 0); font-family: Arial; font-size: 9.3pt; letter-spacing: 0px; top: 0px;display:inline;">coal mines and gambling casinos and other gaming businesses.</div></div>