exception in the past tense clauses sequence rule?

Question

As all of us know as a general grammatical rule,the verb tense in second clause which comes after a simple past tense clause must be in one of the past tenses.

For example:

She knew she had made the right choice.

I touched the baby's head who was crying.

But I wondered when I saw this sentence.

I heard a little boy waving his hands above the water.

I saw a little boy drop his ice cream

Shouldn't it be:

I heard a little boy was waving his hands above the water?

I saw a little boy had dropped his ice cream.

Are there any exceptions to this grammar rule? If yes,what are those specific verbs ?

Answer 1

I heard a little boy waving his hands above the water.

This sentence is fine. "A little boy waving" doesn't violate the rule you stated because it's not a finite present tense verb phrase; it's a present participle phrase meaning it describes an action in progress at the time of discourse. Thus, this sentence means the subject ("I") heard the sound of a boy who was currently in the process of the action of waving. This could be equivalently stated as:

I heard a little boy who was waving his hands above the water

But there is a slight difference between the original and this one. The original implies the sound being heard is caused by the waving. The other version only connects the sound to the boy.

Your proposed alternative:

I heard a little boy was waving his hands above the water

actually means something slightly different. In this case, "heard" becomes a verb of indirect reporting and the speaker is reporting that a little boy was waving his hands above the water presumably based on what someone else told the speaker.

Answer 2

I heard a little boy waving his hands above the water.

This sentence, as you suspected, could be incorrect. It all depends on how you meant it. If you are saying that you were listening to him wave it, then it would be a correct sentence. Because you are hearing the wave. Heard is a past subjunctive in this form.

If you are saying that you heard the boy, who can be defined as someone who was waving previously, then the following sentence will be correct.

I heard a little boy who was waving his hands above the water.

In this form, heard is past tense.

I saw a little boy drop his ice cream.

This sentence can be explained in the same way. saw is a past subjunctive.

I saw a little boy drop his ice cream.

It's explaining that you are in the act of watching him drop the ice cream. You saw the drop, not the boy.

If you had seen the boy, and could define him as someone who had dropped his ice cream, then you could say:

I saw a little boy who had dropped his ice cream.

In this form, saw is past tense.

As for switching tenses, read this article if you want more about it, but it can be a slippery slope and is not usually perfected easily.