If I'm understanding Tsundoku's answer, the claim is: "since even scholars agree that defining periods and movements is challenging, we should not have tags that specify periods and movements." I disagree with both parts of that claim.
First, one can acknowledge that a term is imprecise while still relying on it as a very useful, commonly understood heuristic. Indeed, scholars do this all the time. I don't know any literary scholar who would say that we shouldn't use terms like "modernism" or "beat generation" to characterize movements that belong to the same time period and share some broad features. Yes, Vendler mentions "well-known difficulties of periodization", and then lists a few of those difficulties. But she doesn't go on to dismiss the usefulness of periodization entirely. Indeed, the rest of her essay argues that twentieth-century American poetry can and should be periodized. Her proposed division is as follows:
- Modernism (Marianne Moore, William Carlos Williams), through World War II
- The Age of Auden, a brief 1950s post-war period
- The age of the Beats / vernacular poem / Freudian poem, roughly the 1960s
- The age of the poem of the decentered self (1970s onward)
Her essay having been written in the early 1990s, Vendler's schematic stops here.
It seems to me, then, that Vendler's essay undercuts rather than supports Tsundoku's claim. Vendler tries to come up with a periodization because despite the difficulties, it is useful to do so. Nowhere does she claim that we should not be using terms like "Elizabethan literature" or "Modernism". On the contrary, after rehearsing the problems with periodization for nearly two pages, she ends with: "temporal generalization is incorrigibly necessary to discussion" (p. 234, emphasis added).
Vendler doesn't even go on to make any arguments supporting this last statement, presumably because to any literary scholar, it would seem self-evident. University departments of (say) English hire based on periods and genres, and their course catalogs list offerings such as "The Victorian Novel", "Anglophone Postcolonial Literature in Africa", "The Poetry of the English Renaissance", and yes, "The Beat Generation". Such labels are assumed to be useful and accurate enough. This is not to say they are assumed to be infallible. They are heuristic.
Let's take an example. If an English professor describes herself as specializing in the Caroline poets, other scholars know exactly what she means. One of those others might ask her which poets she focuses on, the Metaphysicals or the Cavaliers. She might in turn respond that she's more interested in the distinction itself, using boundary-crossers like Carew and Marvell to understand and explain how and why such terms as "Metaphysical poetry" and "Cavalier poetry" are deployed. Her point is not that the labels are useless. Her point is that the labels give us a useful and necessary starting point to study both the poets to which those labels apply, and the labels themselves.
In other words: it is a perfectly valid literary question to ask (1) what label is appropriate for a period, a genre, or a movement, and (2) what the limits of that label are, both (a) as applied to a particular writer or work and (b) as a descriptor for the entire group of literary works thereunder subsumed. Such questions are complex; but "one should therefore eschew the use of those labels" is a supportable conclusion neither deductively (it doesn't logically follow from the premise), nor inductively (it's not borne out by what students of literature actually do in practice).
Second, the above answers the question regarding whether we should have tags that specify literary movements or periods. I don't actually see it as a drawback if, as Tsundoku says, adding such tags "would cause a lot of discussions about these tags". Um, the discussion is the point? We already have a tag english-renaissance-theatre that refers to a specific period. Besides, we have tags for genres like short-stories and poetry that raise similar questions about the applicability of labels: does a novel in verse such as Eugene Onegin or The Golden Gate count as poetry? How about Shakespeare's plays? And we recently undertook a retagging effort to specify russian-language rather than russian-literature after discussing precisely such label-applicability questions. (Personally I'd've gone with russophone-literature myself, but that's just me.)
I would even argue that the absence of tags about movements and periods potentially impoverishes our site. For example, if we have a question about, say, Charles Reade, and a Victorian specialist happens by the site, [st]hey? might be able to answer it; but it's not intuitive to search narrowly for Reade, who is no longer that well-known, whereas it's intuitive to say, "H'm, I wonder what questions this site has about Victorian literature". But right now, there isn't a way for someone to search for all the questions that have been asked about victorian-literature. So paradoxically, because we fear that such tags are naïve, we might lose out on expertise.
Is our tagging approach high-maintenance? More so than other sites? I think if a tag is useful, we should use it. And if people are using that tag, it's likely useful to them. I haven't been very involved with tag management here or elsewhere, so I'd appreciate an explanation of what makes our approach more high-maintenance. My sense, however, is that insofar as groupings by period and genre are the norm in literary studies, we should have those tags even if it makes more work for us as a community. It might be convenient to lump Sophocles together with Cavafy because both are greek-language, or in my preferred terminology graecophone-literature; but it makes more sense to say the former is classical-literature and the latter new-athenian-school or modernism or lgbt. What counts as LGBT literature, and whether Cavafy operated within a distinctive tradition that can be so identified, or whether he can be retrospectively seen as pioneering such a tradition, or whether it's politically empowering but historically suspect to think of him as part of an LGBT tradition, are all open questions. But that's reason to keep the tag rather than burninate it.