Hm, jotting down some points of interest. I should really put a "pedantic language nerd" warning on this blog.
As I'm making my way through Le Morte D'Arthur by Mallory, though I'm reading a Modern English translation, there are some artifacts of Middle English that caught my fancy enough to look up. (Btw, disclaimer, I never studied medieval literature, and I'm only interested in language in a general linguistics capacity, so I'm definitely not approaching this from a solid background of Chaucer or anything.)
A particularly fascinating construction I'm coming across in Middle English is the "impersonal verb". This will probably seem pretty sensible to anyone familiar with French/Romantic reflexives, but it does shed light on some fossilised terms such as the Shakespearean "methinks".
Examples of the impersonal verb use:
"methinketh"
"him liketh"
"him reweth"
Characterised by a third-person singular verb (thinketh, liketh, reweth). However, they do not function as regular sentence constructions, for if they were a straightforward cause of a subject + verb, we would use a subject in the nominative case. I.e. in English, "I think, he likes, he rues". But instead, the accusative/dative cases are used ("me" instead of "I", "him" instead of "he").
This is intentional, apparently, and not an archaic grammatical quirk. the impersonal construction shows the action being performed back on the original pronoun, and importantly, dropping an implied subject. E.g.:
me thinketh = (it ) seems (to) me
him liketh = (it) likes him = it pleases him
him reweth = (it) pains him = he rues
Very similar to a French reflexive verb (e.g. "je m'appelle", "je me souviens"-- in fact, I wonder if it was an imported grammatical structure from Norman/French?), but it drops a pronoun, which makes it harder to parse. We don't have this construction in Modern English, but it has become fossilised as a set phrase in "methinketh" or "methinks". However, it's often wrongly used.
The verb "think" stems from two Old English verbs that are extremely similar:
1. thenken --> to think
2. thynken --> to seem
(
Read more here.) So in the Shakespearean sense, "The lady doth protest too much, methinks" is not Hamlet thinking aloud for our narrative benefit, but that it seems to Hamlet, that Gertrude is protesting too much. A neat little leftover from Middle English. :)