philosophy: The Greek word philosophia included everything from Plato's ideas about existence to religious teachings of false religions. Paul does not criticize philosophy itself, but only empty philosophical ideas that oppose the good news.
the spiritual forces of the world (also in 2:20): This phrase might refer to basic teachings common in this world (see Hebrews 5:12), or to spiritual beings believed to have powerful influence over historical events (see also Colossians 2:15, 20; Galatians 4:3).