Kaplan was born at
French Hospital in New York City on March 3, 1941, and grew up in
Lawrence on
Long Island. He studied at
Duke University, and earned a bachelor's degree from
The New School for Social Research. He later studied at
New York University School of Law. Kaplan's interest in Mahler's Symphony No 2 dated back to 1965. In 1981, he began tutelage in conducting with Charles Zachary Bornstein. He rented
Avery Fisher Hall in New York for his public conducting debut in 1982, leading the
American Symphony and the Westminster Symphonic Choir. Originally, the orchestra had requested that no reviews be published, but Leighton Kerner of
The Village Voice breached this requested embargo with a positive review of this performance. Subsequently, Kaplan conducted Mahler's Symphony No 2 in over 100 live performances over the remainder of his life. Mahler's Second Symphony was the only complete work he conducted in public, although he did separately record the
Adagietto from Mahler's
Symphony No. 5 in a studio recording. Kaplan owned the autograph manuscript of Mahler's score of his Second Symphony and published a facsimile edition of the score in 1986.
Tim Page wrote in
The New York Times: "Only now will musicians, scholars and the general public be able to own a facsimile manuscript of one of the composer's symphonies." On 29 November 2016, the manuscript was sold at auction for £4,546,250, a record for any music manuscript at the time. He also owned one of Mahler's batons Both manuscripts were, at one time, on deposit at the
Morgan Library & Museum in New York City. He was co-editor of the new critical edition of the Second Symphony as part of the Complete Critical Edition of Mahler's works. Kaplan's conducting attracted criticism and praise, most controversially at his December 2008
New York Philharmonic performance. Steve Smith wrote in
The New York Times of this concert: David Finlayson, a trombonist of the New York Philharmonic who performed at this concert, offered a different perspective: In Kaplan's conducting engagements of Mahler's Symphony No 2, he did not accept a fee. and in 2000 became an Evening Division faculty member at the
Juilliard School. ==Kaplan Foundation==