I saw that the tree was swaying in the breeze.

[sitifan]

1. I saw that the tree was swaying in the breeze.
2. I saw the tree swaying in the breeze.

The above sentences are quoted from Xuan Yuanyou's English Grammar. Are they both acceptable to native speakers?

[Yankee]

Yes.

[jutfrank]

They do not have the same meaning. Before we begin to discuss this, please tell us what point Xuan Yuanyou was trying to make by comparing them.

What do you mean by 'acceptable', by the way? Obviously, they're both grammatical, if that's what you mean. Why would you read a grammar book that you suspect contains ungrammatical sentences?

[sitifan]

They do not have the same meaning. Before we begin to discuss this, can you you tell us what point Xuan Yuanyou was trying to make by comparing them.What do you mean by 'acceptable', by the way? Obviously, they're both grammatical, if that's what you mean. Why would you read a grammar book that you suspect contains ungrammatical sentences?

1. I saw that the tree was swaying in the breeze . [S V O（noun clause）]

2. I saw the tree swaying in the breeze. [S V O C]

Mr. Xuan thinks that #2 is a reduced form of #1 and they have the same meaning.
Could you tell me what the difference in meaning between the two sentences is?

Though he is not a native speaker, Mr. Xuan is a very famous English teacher in Taiwan and many English learners buy his grammar book and hold him in high repute. As a Taiwanese teacher of English, I think I need to read his book.

By "acceptable," I mean "grammatical and idiomatic."

[jutfrank]

Could you tell me what the difference in meaning between the two sentences is?

I'll try:

In 2, the tree is the grammatical complement (direct object) of the verb saw. Semantically, that means that the tree is the thing that was visually perceived. This is a very direct kind of visual experience—light waves reflected off the surface of the tree and hit my retinas.

In 1, the complement of saw is a that-clause. Semantically, that means that it was some kind of visual evidence of the fact that the tree was swaying in the breeze that was perceived. That's not quite the same, as it may not necessarily have been a direct perceptual experience of the tree in the same way as in 2.

The semantic difference that we have here would be much clearer if we were to replace the verb saw with the verb heard. Try doing that to get the difference in meaning that I'm talking about.

[Tarheel]

1. I saw that the tree was swaying in the breeze.
2. I saw the tree swaying in the breeze.

It's hard for me to see a meaningful difference between the two sentences. However, I am not a professional teacher of English. (Most people aren't.)

I saw the trees swaying in the breeze
The leaves were falling off the trees.
The birds were flying from here to there.
They seemed to be everywhere.

[GoesStation]

They're distinctly different. Number two reports something the speaker has seen with their own eyes. Number one could report that, but it's just as likely to be reporting something the speaker heard or read.

[Phaedrus]

1. I saw that the tree was swaying in the breeze.
2. I saw the tree swaying in the breeze.

The difference can be described as one of visual perception (what the speaker saw was the tree swaying in the breeze) versus apperception/observation (observing that . . .) occasioned by visual perception (as in (1)) or other visual evidence (e.g., a written report about the tree's swaying). Compare:

(A) The police officer saw the driver speeding and checked his radar to verify that the driver was in fact speeding. ["speeding" = exceeding the speed limit]
(B) The police officer saw that the driver was speeding -- his radar told him so -- and he decided to pull him over.

[kadioguy]

1. I saw that the tree was swaying in the breeze.
2. I saw the tree swaying in the breeze.

a. to become aware of somebody/something by using your eyes.
b. to understand something.
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'Saw' in (1) can mean either (a) or (b), while 'saw' in (2) only means (a). Is that right?

[tedmc]

1. I saw that the tree was swaying in the breeze.
2. I saw the tree swaying in the breeze.

a. to become aware of somebody/something by using your eyes.
b. to understand something.

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'Saw' in (1) can mean either (a) or (b), while 'saw' in (2) only means (a). Is that right?

I don't think it has to do with understanding. The second is a direct, sustained visual perception. The first could be a fleeting perception which needs to be corroborated by other evidence as stated by Phaedrus.