Learn Finnish: Jos mies ei olisi loukkaantunut, hän ei olisi kärsinyt niin paljon. - If the man had not gotten injured, he would not have suffered so much.

It uses three parts: the negative verb (ei), the conditional auxiliary verb (olisi), and the active past participle of the main verb (loukkaantunut). This translates to 'would not have gotten injured'.

Does the auxiliary verb olisi change depending on who is doing the action?

No. In negative conditional sentences, the auxiliary verb olla is frozen in the 3rd person singular form olisi for all persons. Only the negative verb changes. For example, 'I would not have' would be en olisi.

Why do the main verbs have different endings, with loukkaantunut ending in -nut and kärsinyt ending in -nyt?

These are active past participles, and their endings are dictated by vowel harmony. Loukkaantua contains back vowels (a, o, u) so it takes the -nut ending. Kärsiä contains front vowels (ä, y, ö) so it takes the -nyt ending.

How do we know these hypothetical events are in the past rather than the present?

The use of the auxiliary olisi alongside the past participle places the hypothetical situation in the past, just like 'would have' in English. A present hypothetical ('would not suffer') would drop olisi and add the conditional marker directly to the main verb: ei kärsisi.