Grebanier was friendly with other drama critics in the greater New York City but perhaps none was a better friend than New York Evening Post editor and chief drama critic Joseph Cookman.
[2] Grebanier's classes "were the most popular at Brooklyn" between the end of World War II and his retirement in 1965.
His method of teaching involved a line-by-line reading of Shakespeare's plays, interspersed with commentary on art, politics, and human psychology.
Most influential of his books are "The Heart of Hamlet," "The Truth About Shylock," and "Playwriting: How to Write for the Theatre": In these books he respectively 1) characterizes Hamlet as misunderstood by critics, as the hero is neither passive, delaying, crazy, nor acting crazy, but rather a Renaissance man who tackles the difficult task of proving Claudius guilty and then proceeds to exact revenge; 2) maintains that Shakespeare does not pursue the question of anti-Semitism in "The Merchant of Venice" but rather uses the stereotype of the Jewish moneylender to ask critical questions about cold-hearted bankers and human compassion; and 3) in a comprehensive textbook, discovers principles regarding the structure of drama that are still taught in creative writing courses across the country.
Grebanier was briefly a member of the Communist Party but soon became embittered and disillusioned about it.