When one conceives of an object in a particular way merely because it is in one's nature to do so, the conception is non-optional and unavoidable.

Placing my hand on a table, my tactile sensation immediately leads my mind to a conception or apprehension that I am touching a hard object. When does one's conception of an object as having a particular quality amount to a perception, a conception accompanied by a conviction of its accuracy? The answer is: when one comes to have that conception because one has encountered a natural sign which leads one to the conception, and that natural sign leads one to the conception merely because of one's