Questions 5 and 6 deal with goodness and the goodness of God respectively. Thomas uses Aristotles definition of good as ”what everyone desires”, which for Thomas obviously is God. Thus God is what everyone desires and everything good participates in God as the supreme good.
The argument has its clear merits – it connects the good with God in a way that secures God’s primacy – i.e. the point is not to absolutify ”the good” as God. God remains God, and the connection rests, I guess, on the fact that as his creatures everyone properly, though perhaps unknowingly desires communion with God, which thus is our good. Also, it avoids the common pietistic mistake of turning God into a separate entity only incidently connected to good – that is he could have been otherwise.
I just wish the argument would have run in the other direction. Rather than proceeding from Aristotle’s definition of the good I would wish that it would have started with God. The end result is the same – the point that everything good participates in God is clearly what is important here – but the way Thomas does it makes it vulnarable to the simple criticism of attacking the definition. It certainly seems that what most people desire is perhaps not the good in the way Thomas means.
Although obviously there might be a lot more at stake here than what I know.