igitur

Igitur draws a conclusion, 'therefore, then', and it is postpositive: it normally stands second in its clause rather than first, so you get hoc igitur verum est and not igitur hoc. Sallust breaks that habit often enough that you will meet it leading a sentence, but second position is the safe default. Quid igitur? is a stock phrase meaning 'what then?'. Compare ergo, which happily leads, and itaque, which always does.