So the clause "it happen" is acting as a noun.

But what is the mood of "happen"? Is it infinitive, subjunctive, indicative, or ... ?

Your post reminds me of an old joke.



A tourist was lost in New York City. He stopped and asked a local citizen how to get to Carnegie Hall. The advise he got was: "Practice, young man. Practice!"

My Chomskyan theory is a bit out of date, but here goes.

Assumptions.

Every verb that has tense and number has "inflection." That's number, tense, aspect, gender, person. You may not see them all ("saw" is the same for all numbers and persons) but put them in if you ever need them anywhere. Keep it consistent.

Verbs have places to be filled, typically by meaning. "See" can be written see(x,y). I'll write it ______ see _______. Meaning assigns roles. Let's skip those here. "Subject" is grammar, not a role. Roles can be filled, depending on the verb, by a phrase. So the roles could be "I see it" or "I see that it is happening."

Nouns need case to surface. No case, no noun slips out of your mouth. "Case" is the difference between "he" and "him" and "his." Where do nouns get case? Often from verbs. Often from "tense."

Verbs assign accusative case to objects, most of the time. Tense assigns nominative case. "I saw him" is built on two levels: meaning assigns "I" the role of perceiver and "him" the role of perceived; but it's tense that gives nominative case so I say "I" (and not "me&quot and "see" that makes "he" into "him." But remember: No tense, no nominative case, and if there's no case you can't say the noun.

"I saw him" winds up having a tree. Inflection says "1st person, past tense, singular, indicative mood, etc.) and assigns nominative case to "I". The verb "see" says what role "I" has and what role "he" has, and says "he" has to be "him," accusative case. But "see" allows for a verb phrase.

If there's a verb phrase there can be inflection. "I saw (verb phrase)" with an inflected verb phrase turns out to be things like "I saw that he petted the cat." "Pet" is pet(x,y), x is the person doing the petting and y is the thing petted. You could write it ____ pet ____. Because inflection has past tense, "he" gets nominative case and since "he" has case the word can be said. "Pet" gives "the cat" accusative case and lets you say it.

English lets you drop out the word that screams, "Hey, here's a subordinated verb phrase" so you could just saw "I saw he petted the cat."

Notice that all's still well. (I saw (that (he petted the cat) )) or (I saw ((he petted the cat)). "Pet" rules the nouns it gives roles to, gives "the cat" acc. case, and the tense on "pet" says "he" is nominative. Tense on "see" says "I" is okay, and the verb "see" gives a role to the verb phrase after it. Does it assign case? Let's say no, that the verb phrase isn't a noun.

Here's a bit of negative evidence: You can't say "I saw him petted the cat." "He" gets meaning from "pet," case from the tense on "pet," and there's no way or room for "see" to touch "he." You work from the bottom up. First the embedded clause, "he petted the cat", then worry about see.

So what about "I saw it happen"? I'll get there. Let's look at a harder example that *shows* what case "it" has. After all, "It saw me" and "I saw it" doesn't show any change in "it". I want you to see that there *is* a change. It's meaningful.

Let's try "I saw he petted the cat" and "I saw him pet the cat." I can never say the following: I saw him petted the cat, I saw him pets the cat, I saw him will pet the cat. I can say: I saw him pet the cat, I saw him petting the cat. What's the difference?

"Petted, pets, will pet" all show tense. Tense assigns nominative case. "Pet" and "petting" show other bits of inflection but don't show tense. No tense, no nominative case. "Pet" still says "I need two nouns, one to do the petting and one to be petted&quot , it can still assign accusative case to the noun after it ("pet the cat&quot .

So "pet" has a problem. It has a role that it must fill--there must be a petter if I don't piddle with the grammar a bit more. But whatever's in that role must have case.

(I saw (he pet the cat))
nom. T ?? no T! acc.

How can we make "pet" happy and get "he" to have case?

Wait. "See" can assign accusative case! So we can let "he" get its meaningful role from "pet" and let its grammatical marking be accusative, assigned by "see":

In other words:
Meaning: (I saw (he pet the cat))
Grammar: (I saw him (pet the cat)).

If you do it that way you have what Chomsky called "exceptional case marking." "See" assigns case across a verb boundary. Ten years later he decided he really hated that idea.

By then he needed all kinds of other things. For assorted reasons, he had proposed (well, others did, and he blessed the idea) two silent pronouns. One was "pro", for languages like Spanish where you drop pronouns. Or English diary style. "Today went to visit McDaniels. Told him to keep his hands off my wife." You assume "I".) You could say those pronouns. The other was PRO, which had the property that it was a pronoun and had to get its meaning from someplace else, had to have a role to give it a purpose, but could never, ever have case and could never, ever be said out loud.

If it couldn't ever have case but needed a role, the prime place for it was as subject of a tenseless verb. Which is exactly what we have in "I saw (he pet the cat)." But it needed to get its referent, what it stands for, from someplace else. The result was

(I saw him (PRO pet the cat)).

"He" has to "move" out of its phrase to get case from "see". What's left is a placeholder PRO. But in "I saw he petted the cat" there's no need for "he" to move. Tense gives "he" nominative case. What happens to the accusative case that "see" has to assign? Leave it empty.)

In fact, this would usually be written as a kind of tree showing all inflection (tense, number, etc.), and showing other things. There are "dialects" of this theory, depending when you learned it and who much of the latest and greatest theory you accepted.

Notice that (I saw him (PRO pet the cat)) also handles ("I saw him (PRO petting the cat)) because "petting" also lacks tense.

A bit of the theory says that any noun also has a spot where it can assign "genitive" or possession. That would get you (I saw him (PRO pet his cat)), where "his" equals whatever PRO means, but PRO gets meaning from "him". Or (I saw him (PRO pet her cat)) where "her" is somebody else. The point is that there are all kinds of places where Chomsky said, for a while, you needed PRO. He disposed of it, I think--there were suggestions to ditch it and have another mechanism to handle things. Don't know where that kerfuffle finally wound up.

Anyway, to your sentence. You'd have to simplify things to say "happen" assigns roles something like _______ happen. Just one place. (That's wrong. Less simplified: happen _______, but "happen" cannot assign accusative case and more stuff has to, uh, happen.)

Simplified:
syntax: (I saw it (PRO happen)). No case from 'happen', case from 'see' and from the tense on 'saw'. 'Happen' has no case to assign, and no tense to assign case.
meaning: (I see (it happen)). 'See' needs a perceiver to do the seeing, something perceived--it can be a verb phrase, an event. 'Happen' needs to have something doing the happening.

If you want it a bit more complicated:
meaning: (I see (happen it)). With the same text: 'see' needs a perceiver and something perceived, 'happen' needs something to happen, and that has to follow the verb.
syntax: (I see it (PRO happen t), where "it" can't be after happen because it needs case and 'happen' can't assign accusative. So it moves in front of the verb, but 'happen' has no tense to give 'it' case, so 'it' continues on its search for validation and gets case eventually from 'see.'

Why do I put 'it' after "happen"? Because happen only has one role to give: what's happening. And I can easily say "It happened that he petted the cat." "That he petted the cat" takes up the one role that 'happen' has to offer, and it's there. Where did that other "it" come from? Rule in English: You need to have the verb in second position. For some verbs we put in a meaningless "it", for others we use "there". 'Happen' can take either, but the word has to change meanings. We need this rule in lots of other places, so it's a sort of freebie.

I don't understand your explanation. Perhaps I am inferring something you didn't mean.

The "it" in "It rained last night" is merely a placeholder, but it seems to me that the "it" in "I saw it happen" is a pronoun and must have an antecedent, which would be some previously introduced event, like "Jim ate his lunch" or "Someone sideswiped your car".

If you asked how I knew your car had been sideswiped, I might reply "I saw it happen". Here "it" clearly stands for a specific event, the sideswiping of your car. I agree that "it" gets its (accusative) case from "saw", which in the English syntax class I took would be analyzed as

(past) + "see" --> "saw".

Syntactically there are only two tenses in English: past and present. Only the first verb in a compound verb is inflected. The idea of future is implied periphrastically. Indicative mood in active voice starts with a sequence like the following

noun tense {modal} {have + -ed} {be + -ing} verb

which undergoes a transformation to produce what older grammarians called a tense, e.g., I eat (present), I am eating (present progressive), I have eaten (present perfect), I have been eating, I will eat (future), I would eat, I had eaten (past perfect), etc. Here tense, -ed, or -ing applies to the following verb. Syntactically and historically, the past tense of "will" is "would", of "shall" is "should", and similarly for the other modals. Curly braces surround optional elements.

The trouble with Noam Chomsky is that he keeps changing his mind. His ideas are a moving target.

I agree that "happen" doesn't have a tense in my example. After that, I get confused. Maybe "saw happen" is a compound verb, or maybe "it happen" is a clause. I'm not sure about this.

"I saw" - subject clause. First person singular, preterite tense of verb "to see"
"it happen" - object clause. Third person (neuter) past subjunctive of verb "to happen"

but that requires a separate main verb. What in your opinion is the main verb in the sentence, "I saw it happen"?

Also, subjunctive mood in English is usually said to be paraphrastic, so that, e.g., "it may happen" is present subjunctive, whereas "it might happen" is past subjunctive. But syntactically "it may (might) ..." is just like "it can (could) ..." or "it will (would) ..." (or any other expression involving a modal). Thus such categories as subjunctive and future would seem to be semantic, not syntactical.

"I" is the subject and "it happen" is the object clause.

The past subjunctive use in this case is triggered by a present lack of reality—the sentence implies that it really did happen in the past, but it is not currently happening at the moment, and thus is un-real at the moment. That state of current unreality triggers the past subjunctive.

that the main verb is "saw" and that "I" is the subject of the sentence.

I tend to agree that "it happen" is an object clause, but other interpretations are possible.

I doubt that the verb "happen" is a past subjunctive, but you may be right about that as well. As Igel pointed out in post #5, your explanation depends on your theory. Traditional grammar and Chomskyan transformational grammar, for example, may yield different interpretations of "I saw it happen".

I haven't delved too deeply into Chomskyan theory on transformational grammar.

I must admit that I had my doubts about this, and still do to a degree. The subjunctive mood has become fairly redundant in English, unfortunately. Few people seem to use it in contemporary English, and those who do are seldom conscious of doing so, let alone explaining it.
My familiarity with the subjunctive comes mainly from my knowledge of romance languages, which actually gave me reason to pause in this case.
"I saw it happen" translates into all romance languages with "happen" being used in the infinitive, rather than the subjunctive.

For example:
French: "j'ai vu ça se passer" or "je l'ai vu se passer"
Italian: "l'ho visto succedere"
Spanish:"lo vi pasar"

"I saw him eat" translates as "L'ho visto mangiare" (Italian) or Je l'ai vu manger (French), or "lo vi comer" (Spanish)

So, I don't want to commit to my previous answer, yet. I did email an English professor who confirmed my original determination that it was "past subjunctive", but I'd like a second or third opinion on that.