Learn Spanish (Spain): No me saludó; no me habría visto. - He didn't say hello to me; he probably hadn't seen me.

In Spanish, the conditional perfect is often used to express a guess, probability, or deduction about the past. While no me habría visto literally translates to 'he wouldn't have seen me', in this context it acts as the conditional of probability. It translates naturally to 'he must not have seen me' or 'he probably hadn't seen me'.

If I want to say 'he hadn't seen me' as a definite fact, what tense would I use?

To state a fact without guessing, you would use the pluperfect (past perfect) tense: no me había visto. By choosing the conditional perfect habría visto instead, the speaker makes it clear that they are just making a deduction about why the person didn't say hello.

If the second half of the sentence is a guess, why doesn't it use the subjunctive mood?

You only need the subjunctive when using specific phrases that trigger doubt or probability, such as dudo que or es probable que. When you use the conditional tense itself to express probability, no external trigger phrase is used, so the verb remains in the indicative mood.

Why is saludó in the preterite tense rather than the imperfect?

The failure to say hello happened at a specific, completed moment, such as when passing each other on the street, so it takes the preterite saludó. Using the imperfect saludaba would change the meaning to describe a repeated habit in the past, meaning 'he didn't use to say hello to me'.