In an effort to assist a Japanese speaker learning English I was asked a grammar question that I was not easily able to explain. The question was a "why" question, specifically with causative verbs. The example used was:

* I made him go.
* I let him go.

These use bare infinitive verbs. In these two cases, the word "to" is not needed.

Incorrect:

* I made him to go.
* I let him to go.

Then there was the question with the words order and ask.
With the following two sentences, the word "to" is required:

* I ordered him to go.
* I asked him to go.

In these cases it is not correct to say:

* I ordered him go.
* I asked him go.

Now comes the hard part.

1. Why? What's the difference?
2. Are causative verbs so special?

Easy answers:

1. There is a rule with certain words like ask and order.
2. Yes.

Harder question:

1. Why is there a rule with order and ask?
* Note that with most answers given you will be able to say, but you don't use "to" with made or let or but you must use "to" with ordered and ask, so what's the difference?

There is one observation I did make that may not explain the why part but since it was a difference between the two examples, this appeared to help the person understand.

I the case of ("made" him go) or ("let" him go) I believe it can be assumed correctly that the person "went". However, with I ordered, or I asked (him to go) the result of if he went is not 100% known. This is a difference, yet I do not know if it explains the why part. I also thought that the "to" was needed to connect the action (ordered/asked), but then why is "to" not needed to connect the action in the case of (Made him go/Let him go)? I thought maybe "to" is implied with made and let, but then thought, why is it not implied with ask and order? Maybe because the result is not known?

For an English speaker it is easy to say what just sounds correct because it is our own language and we can associate the sounding and feeling of "correctness" but to try to explain the reasoning to a non-native English speaker, the challenge becomes increasingly difficult. Maybe there is an answer somewhere. I can say the answer is probably that "It was decided at some point in time." This answer would be correct in most cases for any question but the follow-up question of course is "Why?"

seraglyph

“but to try to explain the reasoning to a non-native English speaker, the challenge becomes increasingly difficult.”

Sometimes there is no reason.  Stop banging your head against a wall.  It's a waste of time.

Research "catenative verbs" and you will find that, while there are some vague principles underlying the differences you're interested in, there is hardly ever a clear reason that might be pedagogically useful.  Save such discussions for very advanced linguistics students.  Less advanced students only need lists of verbs that fit into each pattern.  And practice. 

CJ