The scientific method has proven to be the most reliable and successful method of thinking in human history, and it is quite possible to use scientific thinking in other human endeavors. Critical thinking--the application of scientific thinking to all areas of study and topics of investigation--is the key to the advancement of humanity. Critical thinking involves distinguishing between fact and conjecture; distinguishing between an idea and the name of that idea, and providing definitions; looking for (hidden) assumptions and performing hypothetico-deductive reasoning. Critical thinking is thinking with scepticism about a subject or field.

Thinkers must keep very clear in their minds what they know, what they think they know, what they are suspicious of, and what they want.