- Let he who believes in this prophet speak now what he knows.
- Let him who believes in this prophet speak now what he knows.
To analyze this situation, it helps to separate the who clause (who believes in this prophet) from the main clause (let him/he now speak what he knows) and then analyze each clause separately.
Since let him speak now is correct, let him [who believes] speak now is also correct; and since let he speak now is not correct, let he [who believes] speak now is also not correct. Your second example is therefore the best one, grammatically speaking:
"Let him who believes in this prophet speak now what he knows."
Ngrams shows that Let him who is also significantly more common than Let he who:
Ok, let's look at this in terms of grammar. After all, the question asked which sentence is grammatically correct.
First, let's get rid of some words that may be confusing the issue. "Who believes in this prophet" is describing, or defining, he/him. It is a restrictive clause. Its only purpose is to define he/him. As a restrictive clause, it is a descriptive clause. We can remove it to figure out the him/he problem.
So what is he/him in this sentence? It is the direct object of the verb "let." As with any object, he/him is answering the question "what?" (for non-people) or "whom?" (for people). This gives us "Let what?" and "Let whom?" The answer to the question is an object.
Ok, so we need an object pronoun because the word is serving as an object of "let." What are the object pronouns? They are: me, you, HIM, her, it, us, them.
Look! "Him" is an object pronoun, so if we need an object, which we do in this sentence, we use "him." As such, "Let him who believes in this prophet speak now what he knows" is correct.
But wait a second! Isn't he/him the subject of "speak"? No. If that were the case, we would use "speaks," which is the third person singular form of "speak.' The sentence would read "he...speaks," but it doesn't here.
Now, the simple, practical solution: If we remove all the descriptive expressions from this sentence and pare it down to its roots, we get "Let HIM speak." I dare anyone to say "Let he speak" is correct.
Neil: Regarding speaker's judgment and usage: Sure, people can, and do, speak any way they choose. However, the question was about grammatical correctness. I'm not sure what "clause" you're referring to, but your example also demonstrates the point I'm making. In your example expression "They hoped for him to win," again, we see that "him" is serving as an object--in this case as the object of the preposition "for." We can ask, "For whom?" The answer will be an object.
If you need an object, whether the object of a transitive verb or the object of a preposition, your choice is "him," not "he." "He" is a subject pronoun; "him" is an object pronoun. This confuses many people, so I'll simplify: If you need the subject of a verb, use "he." If you need an object, use "him."
I appreciate David Bowman's answer above, with one exception: he writes,
Isn't he/him the subject of 'speak'? No. If that were the case, we would use 'speaks,' which is the third person singular form of 'speak.
Actually, the "him" is the subject of "speak". I don't know the terminology in English, but it is akin to the accusative subject of an infinitive in Latin (if I remember correctly).
It is very common for a direct object to serve also as the subject of a following verb in its barest form (the "infinitive" in other languages, though usually without the "to" in English):
Watch me do this
Help me (to) do this
Let me do this; etc.
The "me" is the object of "watch", "help", and "let"; and the subject of "to do" (for I am the one 'doing', no?).
I think it's ... Let he who.
Because what is this sentence really trying to say? It's not really about letting anyone do something. it's about who's the most legitimate person to talk about something. if someone were blocking someone's path I would say let him come up to the microphone. but in this case it's not about somebody being restricted. let is a kind of an old-school way for making a generalized proclamation, and is essentially meaningless. It's really a timeless statement. Who should get the job? He who is most qualified. Not him who is most qualified. Who is most qualified? He is. Well, give him the job already.
But that seems to work against my point. Give him the job. But then again this is not about a physical action done in real time. This is not about letting somebody come up to the microphone. This is about the eternal question of who is most qualified, phrased in a specific way. simplify to support the timeless quality. get rid of let. he who is the most qualified should speak, now and forever. not him who is most qualified should speak now and forever.
Sure, there maybe tricky grammar rules against my point. They fail to convince. This is, in the end, an idiomatic expression.
He who is best qualified should speak.
Okay now let's apply it to an immediate situation. Who should speak? That guy over there. Him.
But that changes the whole time and place of the statement to something that isn't what we're talking about. we are not talking about picking the guy out of the crowd to step up to the mic. we are making a timeless philosophical statement.
I am writing this on my phone and capitalization is a challenge so please forgive etc.