I’ve come across writings (including the wanikani context sentences for 思う) that use ‘と思う’ in order to say, “I think…” versus the act of thinking in general, but I can’t find any explanation about the added と in the beginning. Does simply adding と in front of other verbs similarly change its meaning in the same way, or is this something that’s exclusive to と思う specifically?
Moreover, I’m also confused about the meaning of this verb in certain contexts. I’ve seen it translate into things that don’t involve thinking at all - take this sentence, for example: これから日本語を一所懸命勉強したいと思います。- which translates to “I want to do my best to study Japanese.” At first glance I would assume that this sentence translates to “I think I will do my best to study Japanese.” Is the meaning shifted a bit because of したい added before it? Or how would you make sense of this?
と is a quotation particle - it goes on the back of what’s being quoted, not on the front of the verb. So, Xと思う is literally "I think ‘X’ ", though translations can be a bit looser than that. Particles in general are postpositions - they modify the word or phrase that they follow.
But yeah, ～たいと思う is its own grammar construction. It’s a way of softening the ～たい, because on its own it can come across as too strong or abrupt.
It often does change the meaning. The quotative と is like saying “that” in “I think that X”, though in English it’s optional. I’m not sure I’ve seen 思う used with any other particle, but A) I’m personally using it way too often and B) maybe it always needs it, because と思う is a sentence-ender. Some verbs like 感じる、考える and 信じる can take different particles and the meaning is different.
Very good to know! One thing I’m still confused about, though, is how some sentences that use と思う translate to “I think X” even though there’s no actual indication of the “I” in the sentence. I’ve also seen this with other verbs following the quotative と (although, I’m not 100% sure this has anything to do with the quotative と). Take this sentence, for example:
Isn’t that just a fact about Japanese sentences generally? Well, 思う is a little special, in that you usually don’t use the simple present to talk about what other people think, but omitting the subject is normal in Japanese.
This is doubly true for と思う, because you can only use it to talk about your own thoughts. Talking about what you think other people are thinking uses different verbs or conjugations, I think because presuming to know what other people are thinking is considered rude in Japanese. Since the subject then has to be the speaker, it can be omitted.