I don't know what you mean by that, but I have discerned as someone suggested that the odd-numbered ones were up til FF7 focused on gameplay and the even-numbered ones were focused on story. You can kind of see it in the way the battle system went until FF7. FF1, FF3 and FF5 all had the job system, while FF2, FF4 and FF6 showed the characters with stable classes.
Sakimoto himself spoke about how every odd-numbered FF had a class system (I suppose 7 and maybe 9 are excluded) and they tried to get 3 FF games per console. Basically, he was being Captain Obvious.
desides said: Sakimoto himself spoke about how every odd-numbered FF had a class system
I don't know which article, and I'm iffy on if it was at RPGamer, but I had read that the odd-numbered ones were made of the safe side, with a series-norm consistent use of class-based parties and crystals and such, with the even-numbered ones trying something new (for the series).
desides said: Sakimoto himself spoke about how every odd-numbered FF had a class system (I suppose 7 and maybe 9 are excluded)
FF9 definitely had classes, if you define a "class" as having different abilities that are unavailable to other characters (Steiner's sword abilities, Vivi's black magic, etc). Not like in FF10 where you could "break" outside of your class by learning other characters' abilities on the sphere grid...