"It Ain't Necessarily So" is a song from the 1935 musical Porgy and Bess, composed by George Gershwin with lyrics by Ira Gershwin. The song is performed by the character Sportin' Life, who expresses skepticism about various biblical stories and the truths people often accept without question. The song's catchy melody and playful lyrics challenge the audience to think critically about beliefs and assumptions. It highlights themes of doubt and the importance of questioning accepted narratives, making it a memorable piece in American musical theater history.