A definition of thinking:

Definitions are really only descriptions. They’re always less than the thing they describe. So here’s a definition written as a description: thinking involves considering other options to every assumption you’re working with. Thinking involves treating your premises as subjective, not objectifying them. Thinking involves, out of principle, never absolutizing your own perceptions, but ever challenging them. Once any of that stops, you’re not thinking, you’re reacting. And that becomes a tyrrany over the mind, a fascism of the soul, and a depersonalization of the world.