Do you know what you’re hearing?

Let Rob Kapilow be your guide at “Rob Kapilow’s What Makes It Great?’’ The classical music commentator has a knack for pulling themes apart and guiding audiences through musical mazes. Tonight’s program examines Mendelssohn’s Octet in E-flat major with help from the Borromeo and Ariel string quartets. The Borromeo is a longstanding quartet-in-residence at the New England Conservatory; the Ariel is a young Israeli-formed quartet that moved to the United States in 2004 to continue their professional studies at the conservatory. 8 p.m. $25. Jordan Hall, 30 Gainsborough St., Boston. 617-482-6661. www.celebrityseries.org