Do I have to use the perfect infinitive

Question

I was taught that if we had some action which can happen before some moment in the future, I had to use Perfect. For example:

I will have done it by the morning.

Some days ago I had to say a sentence like this:

I will want to (come) by the beginning of the meeting.

And I was stuck because I thought the action "to come" had to be with perfect because it could happen before some moment in the future. It would look like this:

I will want to have come by the beginning of the meeting.

But then I thought it would mean something different because the sentence

I want to have come by the evening = I want so I would have come by the evening

mean that I want something what could have happened in the past but not later the wanting moment, not later than now, not in the future.

The sentence

I wanted to have come

means the same(as I know). I wanted something what could have happened even before the wanting moment, not later than it, not in the future but only in the past.

And If I say:

I will want to have come by the beginning of the meeting

it may mean that I will want something what didn't happen in the past happen in this past. But my sense is the action "to come by the beginning..." is not earlier than the wanting moment, it's in the future.

If I can say for this so:

I will want to come by the evening

meaning that the "come" action is in the future for 'will want", then it's perfect.

If I can say:

I will want to have come by the evening

meaning that the "come" action is in the past for "will want", then it's clear.

If to ask shortly, we have two sentences:

I want to come by the evening

I want to have come by the evening

Are they correct and what do they mean?

Answer 1

The sentence

I will want to have come by the evening.

Implies that you don't want it now, but will later. This is almost surly not the intended meaning.

While it is possible to say:

I want to have come by the evening.

it is awkward and technically incorrect. It would probably be understood, but would not sound right. Moreover, there is another possible sense which is grammatically correct but almost surely not intended, where "come" has a sexual meaning. Anyone thinking of this meaning would be amused and distracted.

As Astralbee indicated, it is much better to use 'arrived' here:

I want to have arrived by the evening.

However, for informal speech, one might better say

I want to be there by the evening.

or

I want to get there by the evening.

The second stresses arrival, the first presence, but in practice the meanings are essentially the same.

Answer 2

Your first example shows the correct use of the future perfect tense:

I will have done it by the morning.

"Have done" alone would present perfect - the rest of the sentence puts it into future perfect. But note that "done" means completed. It is the past participle of the verb "to do".

Your question is about:

I will want to have come by the beginning of the meeting.

This is incorrect. "Come" is the base form of the verb so it does not fit this sentence the same way "done" does is in the previous example.

Your sentence should really say:

I will want to have arrived by the beginning of the meeting.

"Arrived" is most appropriate because the verb "to come" implies movement towards something, so no form of this verb really describes you having completed this journey and arrived at your given time.

This is the case for all your subsequent examples:

I want to come by the evening
I want to arrive by the evening.

I want to have come by the evening
I want to have arrived by the evening.

Both mean the same - that you want to be there by (before) evening. Using the future perfect tense is often a choice, unlike when you are speaking about past and present events when you must use the correct tense else make a grammatical error. The future perfect tense is a different way of speaking about future events, projecting ourselves forward into the future so that we can then look back at an action that will be completed later. It is a choice like using active or passive voice - the meaning is ultimately the same.

Be aware though that this is not a rule for all verbs - some just do not work in the future perfect tense - Come/Came being a prime example. Another is do/done. If you say that you want "to do" something by a specific time it does not necessarily mean you will have it completed by that time, so the two are not interchangeable as one may describe the start and another the end of an action. You should consider each verb and what it implies to see if it makes sense using it in the future perfect tense. If it does not, use a word that more accurately suits the completed state.