a hardening of the arteries and categories??? What is old age? Fundamentally, no doubt, it is a condition of the flesh, of protoplasm that finds inevitably the limit of its life. It is a physiological and psychological involution. It is a hardening of the arteries and categories, an arresting of thought and blood; a man is as old as his arteries, and as young as his ideas. The ability to learn decreases with each decade of our lives, as if the association fibers of the brain were accumulated and overlaid in inflexible patterns. I would like to know what does "categories" mean here ? Thanks.