Both sentences are grammatically correct, but there's a subtle difference in how they use "could" and tense: 1. "There could be a situation where it's clear that they are approaching": This is correct. It's talking about a possible situation in the present or future, which aligns with how "could" is used for real, current, or future possibilities. 2. "There could have been a situation where it was clear that he was at fault": This is also correct, but it describes a hypothetical or unreal situation in the past, which is appropriate when using "could have been" for past possibilities. So, "could" can be used for both real-time and hypothetical situations, depending on the context.

I agree with Albert. The two sentences you use are two types of conditional sentences: 2nd and 3rd. If you look up the different types of conditional sentences, it should help. Briefly: 1st conditional: If you study hard, you will do well on the exam. (Real possibility for the future, uses present tense verbs.) 2nd conditional: If you studied hard, you would do well on the exam. (Similar in terms of time, still possible but more 'imaginary'). This seems confusing, because it uses past tense verbs, the the conditional is in the present tense. 3rd conditional: If you had studied hard you would have done well on the exam. (completely 'imaginary/impossible' because if refers to something in the past that cannot be changed).

Both sentences are grammatical, yes. The use of "could" in your first sentence implies the situation is hypothetical or uncertain, even though it is followed by "be." If you want to express more certainty, you would probably use "can" or "will" instead of "could" (which is actually the conditional form of "can"), ie, There can/will be a situation where it's clear they are approaching. (You'll note I got rid of "that"...in my observation native speakers often omit relative pronouns in situations like this. But it's perfectly fine to leave it in if you like; this is just a personal style preference on my part.) And again, the second sentence also reads fine to me.

Is it correct that the sentences “There could have been a situation where it would have been clear that he was at fault” and “There could have been a situation where it would have been clear that he would have been at fault” are not correct?