articles - Why "the schoolboy" instead of "a schoolboy" in this sentence?

At the same time, however, Walser’s narrators—especially his schoolboys, and there is something of the schoolboy in all of his narrators—are possessed by a levity that borders on giddiness.

(Source).

Why is the used here instead of a? It sounds like its talking about a general schoolboy.

Answer

It would be perfectly correct to use the indefinite article (“a”) here, but the author (Ben Lerner) has chosen not to, instead employing the definite article (“the”).

It's a very fine distinction, and the meaning is essentially the same in either case, but Lerner means to invoke the archetypal schoolboy.

With this choice, Lerner is suggesting an ideal schoolboy who may not actually exist in a single bodily form, but is nonetheless the singular epitome of everything it is to be a schoolboy.

It's that schoolboy that there's something of here. All together, it means that some of Walser's narrators are schoolboys who can be counted and named, and others borrow somewhat from the qualities usually attributed to schoolboys.

As J.R. points out, it means “somewhat schoolboyish” either way you write it. As J.M.L. points out, the definite article structure is an established turn of phrase.

Either phrasing requires agreement among those communicating about the qualities of whichever archetype is invoked. In some cases, this is very simple (“zealot” or “daredevil”, for example), because the descriptor is based on the characteristics in question. In other cases (like “gypsy” or “schoolboy”), what exactly constitutes the character of “the schoolboy” that there's “something of” in whomever else might be a little less certain, but, as always, context should provide sufficient clues.

Long story short (too late), if you're going to use the “something of the [archetype] in [actual person]” format, you're best sticking to the definite article form as it a) is an established turn of phrase and b) will make it clear that it's the spirit of the archetype inhabiting your subject, and nobody's physical parts are in anyone else's.