Mr. Sondheim has always functioned as a theater man first, a songwriter second. Unlike all but a few of his theatrical contemporaries, he has never aspired to write songs that have a pop life of their own; all of his songs reflect the dramatic situations and characters of the musicals they were written to serve. What is more remarkable is how well Mr. Sondheim fulfills this mission. Yank one of his songs out of its original context, and you're often left with a self-contained play.

One example on the new record ["A Stephen Sondheim Evening"] is an eight-minute masterpiece: "Someone in a Tree" from "Pacific Overtures." Its subject, of all things, is the treaty by which the United States "opened up" Japan in 1853. Because there is no Japanese account of what went on in the treaty house where Commodore Perry negotiated with his hosts, Mr. Sondheim imagines how...