Learn English – If you could be any age, what age would you be? Conditional

Compare the following sentences:

Present time

1. It's very dangerous in Metropolis right now. You can be beaten up for just looking at someone the wrong way.
2. It's very dangerous in Metropolis right now. You could be beaten up for just looking at someone the wrong way.

Sentence (1) presents being beaten up as a live possibility, as something that does actually happen to people. Notice that we can analyse for just looking at someone the wrong way, as some kind of condition:

1'. You can be beaten up if you just look at someone the wrong way.

Sentence (2) presents being beaten up as a hypothetical outcome of the wrong look. It is not being presented in the same way as in (1). It doesn't necessarily say that people are being beaten up for looking at people the wrong way - although we might assume that they are.

Could in sentence (2), as already mentioned, represents this outcome as a hypothetical possibility, as opposed to a live one. We could rephrase it as the following hypothetical conditional:

2'. You could be beaten up if you just look(ed) at someone the wrong way.

Remember both of these sentences refer to the present or future time. The way that we interpret you here is quite likely to affect our interpretation of the sentence. It's also quite likely to affect our choice of can or could. If you means a person in general, we are more likely to use can. If you is being used to make the listener imagine themselves in that situation, then we are more likely to use the hypothetical could.

Past time

Let's move forward twenty years. Now if we wish to make the same kind of statement but about Metropolis twenty years ago instead of now, we need to shift the tenses back to indicate past time. Example (1) would now be as in (3):

3. It was very dangerous in Metropolis in those days. You could be beaten up for just looking at someone the wrong way.

Here we see could appearing as the past form of can. This past form of can still implies that people actually were being beaten up for looking at people the wrong way. It is being presented as a live possibility for people at the time. It has exactly the same meaning as can, but refers to a past time. It does not represent hypotheticality.

However, in sentence (2) we already have past tense could, where the past tense indicates hypotheticality. If we wish to keep this hypothetical flavour, but also indicate past time, then we need to shift the tense back further. We need to use a past perfect form as in (4):

4. It was very dangerous in Metropolis in those days. You could have been beaten up for just looking at someone the wrong way.

Sentences (3) and (4) could be construed as the conditionals:

3'. You could be beaten up if you just looked at someone the wrong way.

4'. You could have been beaten up if you ('d) just looked at someone the wrong way.

So if we see a past perfect form could have this most likely represents past time reference plus hypotheticality.

Hope this helps!