Questions & Answers about Minä kertoisin totuuden, jos olisin syyllinen.
Why is it kertoisin with the strong rt instead of the weak rr like in kerron (I tell)?
The conditional marker -isi- attaches to the strong stem of the verb. While adding the personal ending -n usually makes the stem weak (like rt becoming rr in kerron), the conditional marker acts as a buffer. Therefore, the verb kertoa keeps its strong rt to form kertoisin.
Why is the word for truth, totuus, written here as totuuden?
totuuden is the object of the sentence. In Finnish, when an action is complete and affects the whole object, we often use the genitive case, which adds an -n. Notice the stem change here too: the basic word is totuus, but its stem changes to totuude- before adding the -n.
Why does Finnish use the conditional olisin (I would be) for the English 'I were'?
In English, we say 'if I were... I would tell...'. However, Finnish requires the conditional marker -isi- in both halves of an 'if' sentence. So you literally say 'if I would be guilty, I would tell the truth' (jos olisin... kertoisin).
Does syyllinen need a special case ending here?
No, syyllinen (guilty) is in the basic nominative case. In sentences describing what a specific person is (using the verb olla), the describing adjective just stays in its basic form.