Hi! I just finished chapter 1.3 in Hooktheory II and got question:
There is a diagram that shows you that after chord V7 usually comes I (because it sounds really good than other chords), and also there is a diagram that shows you that after iii usually comes IV or vi. So, I can apply this to all keys not only C, or this is work only in C and I must find other chords in other keys thats usually work good together and usually comes after iii or V7 in this keys?
yes, in fact the entire point of using Roman Numerals to discuss these concepts is because they are general, and we want a way to discuss how things work in a way that is key neutral. The tendencies you mentioned above will work in any key.