Is the sentence below correct with respect to parallelism?
Do all nouns need an adjective?
That's how I should have said it.
Still, it falls foul of Strunk & White's 19th principle in their Elements of Style, "Express coordinate ideas in parallel form"; in fact, it's a much bolder violation of this principle than the example that Strunk & White begin their discussion with:
(2) Formerly, science was taught by the textbook method, while now the laboratory method is employed.
Strunk & White continue their exposition on maxim 19 with various types of questionable coordinations, mostly of the sort we've been calling "WTF coordination" here at Language Log Plaza (most recently, in Eric Bakovic's report of a possible Bushism and in my discussion of two specific cases, one involving recipe register features, the other coordinate questions). That is, they lump together rhetorical parallelism and the requirements of syntax. As it turns out, they also work with an implicit, unexamined theory of coordination that's seriously confused. And they cast their advice in very general terms, without seeming to realize that their rules actually make predictions about what's acceptable English, many of which they would surely not welcome.
Strunk & White aren't alone in these respects. As I'll illustrate briefly from two recent manuals, the advice literature on parallelism exhibits all three of these problematic features: a fuzzy notion of parallelism (more generally, a failure to distinguish grammar, usage, and rhetoric), a seat-of-the-pants syntactic theory, and wildly overgeneralized prescriptions.