I have a trouble to determine tense in the following sentence:
The reception would be held in that house.
It is not a future simple, and future, relative to past perfect as I thought.
It is because in the future simple we must use will instead of would.
Best Answer
I'm not sure if this would make sense for you, but it might be better to avoid thinking of would (and even will!) as a tense.
I have two main reasons for that. One is that it could simplify things a lot for learners to think of would and will as modal verbs, rather than to think of them the way we think of other auxiliary verbs (such as be or do) or main verbs, which will normally indicate the tense. (In other words, it's better to think of will/would the same way that you think of shall/should, can/could, and may/might) The other is that it is simpler to think of English tense system as a two-tense one, i.e. past and non-past. (This is too complex to discuss in this question, in my opinion, but it could nudge you in the right direction a little.)
Back to your sentence,
It would be better to have a more complete context, so that we could discuss it more appropriately. However, I think it's enough for our discussion to assume that it's something someone says in a dialogue. Suppose that that is the case. It means that this would is used for saying or asking what someone thinks about a possible situation (sense 3).
In what tense is it? To me, it has no tense. (This might disagree with your grammar books, but it's simpler this way.) It is something someone says in the present while that someone is thinking of a possible situation in the foreseeable future.
Would has several uses. An extremely simplified explanation of would is that it is the "less definite" form of will. It can be used as the past tense of will. It can be used in hypothetical thinking, and conditionals (those if-clauses, particularly those that you might know them as Conditional Type II) can be considered hypothetical. It can be used to put a distance between what we say and the reality, which is a way to make what we say sound more polite, because it's indirect. (For example, "I'd like to ...", "Would you mind ...?")
I hope that that should be enough to cover this question. However, please keep in mind that there might be more to would than what I've just discussed that I might have overlooked.