anoétos adj def lack of wisdom, stupidity arising from deadness and impotence of intellect

pronounced an-o’-ay-tos

Foolish does not indicate a lack of intelligence.  It refers to one who doesn’t use one’s powers of perception or doesn’t reason through a matter.

Here in Galatians, Paul’s expression is a mix of surprise and indignation. He follows by asking a series of questions showing the church how absurd the notion of their Christian lives being matured by self-effort instead of relying on the Holy Spirit’s leadership.