Using Early Modern English, can I have more than one conjugated verb in a sentence? For example, would I be more correct to say, "Thinkest thou that thou could take us to see him?" (Note that only 'thinkest' is conjugated.) Or would it be more appropriate to say, "Thinkest thou that thou couldst take us to see him?" (Note that both 'thinkest' and 'couldst' are conjugated.)
Combining the example in your question with the example in your comment shows a bit of a misunderstanding about the difference between clauses and sentences and therefore the answers to your question.
In English, (any variety) each clause with a verb must have a some kind of verbal inflection (there are some counterexamples to this generalization but for the moment it will suffice).
- *John leave at noon.
- John leaves at noon.
- I/we/you/they leave at noon.
- John/I/we/you/they left at noon.
- John/I/we/you/they will/might/can leave at noon.
- *John might leaves at noon.
In a main clause with just a main verb, the main verb must be inflected. However in the forms of the verb we really on see very limited inflection in the present tense in main verbs, specifically 3rd person singular –s, as in (2), whereas for all other person/number combinations the form of the verb doesn't change.
In the past test, the verb only inflects for tense, and no person or number distinctions are possible.
If we have a modal verb, then the main verb shows up in its bare (uninflected) form. This is why (5) is grammatical and (6) is not. Modal verbs themselves don't inflect for either tense or person/number, as in (5). [would is not the past tense of will for example.] This may be what you mean by "only one conjugated verb in a sentence".
In these examples, there is one sentence and one clause, and therefore one inflected verb (either the main verb or the first auxiliary verb or a modal). But sentences can have more than one clause. Each of the sentences in (1-6) can be turned into a subordinate clause by adding "Bill thinks that ... " to them. But notice when we do that, the pattern of inflection doesn't change at all:
- *Bill thinks that John leave at noon.
- Bill thinks that John leaves at noon.
So in (5) we still have to inflect leave even though we have inflected think. This is because there are two clauses in this sentence, and each verb needs to have its own inflection. This is different from the examples in (5) in which we have a modal verb and then the main verb is uninflected.
Now we can look at the two examples you ask about (one in the question) and one in the comments:
- Thinkest thou that thou couldst take us to see him?
- *Thinkest though that thou could take us to see him? (probably * )
In this pair of examples, we would expect (9) to be possible for sure, since we have two clauses, and therefore both verbs can be inflected. Note that could and other modal verbs inflect for person in Early Modern English, but they only do so for the second person form thou. Looking quickly through Shakespeare, we don't seem to find any instances where a second person modal verb is uninflected, so it is likely that (10) was not possible at the time.
Here is one example from Othello:
- Thou told'st me thou didst hold him in thy hate. (Othello I-1)
The second example, (in your comment) however is different, since it contains only one clause. Here we can be quite certain that the second verb see would not be inflected, since the modal verb would is already inflected. So (11) would be ungrammatical while (12) would be fine.
- *Wouldst thou seest him?
- Wouldst thou see him?*
You can confirm this by searching would such structures in Shakespeare.
- Where didst thou see her? (Othello, I-1)