Robert Burton called it “gut feeling” — “involuntary mental sensations that function independently of reason”. William James described it as “felt knowledge”, something extraordinarily difficult to be dislodged through rational arguments. I call it “intuitive knowledge”.

Cognitive scientists now seem to believe the bulk of our thoughts originate in the areas of the brain inaccessible to conscious introspection. The trick in Chris Nolan’s “Inception” — the planting of an idea in human mind — if it can ever work, we have to sort out where to plant it first. Thoughts arrive in consciousness already coloured with inherent bias. Our perceptions are filtered through our genetic predispositions, biological differences and idiosyncratic life experiences. Your red is not my red. These differences extend to the very building blocks of thoughts. Thinking may be as idiosyncratic as fingerprints.

Illusion is also a form of perception. If you think you can actually see the world as it is, you are in illusion.

Certainty is not biologically possible. We must learn to tolerate the unpleasantness of uncertainty.