Acharya Prashant explains the different grades of the mind. The mark of the commoner is that he lives in his personal world and attributes the finality of truth to it. The common mind is inclined to say something exists because he feels or thinks it does. His world is very subjective. The mark of the scientist is that he does not live in his personal world or care about subjective interpretations; he lives fully in facts. His science is fully objective and contains no trace of personal subjectivity. The scientist is an advancement over the common psyche. The scientist says something does not merely exist because it appears to exist, as appearances can be deceptive and vary. Therefore, he must verify and cross-check, which is the scientific method. While any number of proofs do not suffice to ascertain the veracity of something, one proof against it suffices to prove it false. Then there is the spiritual mind. The mark of the spiritual mind is that it does not lend veracity even to the factual world. The spiritual mind says that not only is the imaginary world unreal, but even the objective, factual, scientifically proven world is not quite real. There is another quality of mind that is below even the common mind: the mind of the madman or the crazy man. The common man cares at least a bit for facts, whereas the crazy man does not care even one bit for facts. The common mind might see a pillar and say, "I do not like this pillar," making it a "dislikeable pillar." The crazy mind, however, may say the pillar is an elephant and insist on this totally personal truth. The more your truth becomes personal, the crazier you are. The madman also lives in truths, but all his truths are purely personal. He does not bother about universality, verifiability, or facts. All he bothers about is his subjective perception. The more you live in your world of subjective perceptions, the crazier you are.