Here’s a thing I learned this week: Ladies and gentlemen, we’ve been using a defective word all this time. Beware. No, I mean the word itself, beware. It’s defective.
Wiktionary notes that beware, as a modern English verb, isn’t doing all that it could do, because we can only use it in the imperative (“Men, beware women with one long fingernail.”) and the infinitive (“I thought I told you to beware that fingernail chick.”) We haven’t been able to conjugate it properly for generations, and I don’t think I’ve ever heard anyone say “He bewares the dog” or “I am bewaring the Ides of March.” But I’d never realized that until this week. That’s probably because modern English allows us to say “He is being aware of the dog” and “I am being wary of the Ides of March.”
As far as English defective verbs go, beware is odd in that it isn’t modal. The other defective verbs are auxiliary verbs such as can (it’s present tense only), could (future tense only), may (future tense only), must (which, according to Wikipedia, once had the past tense mote but no longer does), ought (once the past tense of owe) and might (once the past tense of may). In fact, aside from impersonal verbs that you can conjugate but just don’t have reason to except in poetic contexts (“It’s raining” but rarely “I rain”), the one non-modal defective I found listed anywhere was quoth, which I’m willing to bet most people alive today have only ever heard in “Quoth the raven, ‘Nevermore.’” As Wikipedia notes, it’s actually the past tense of the extinct quethe, “to say,” and which also survives in the form of the word bequeath.