[There is] a difference of [= between] truth and habit. For the truth is discovered by making a genuine and complete search. But habituation, whatever is accepted, whether it is true or false, is uncritically confirmed by itself. But the person accepting such a habituation is neither delighted at what is true nor grieved by falsehood. For such a person has not trusted his judgment but his preconception,[1] and has bestowed his own expectation on the understanding of what is before him, making use of an unproved chance. And it is impossible easily to get rid of the inherited assumption, even though such assumption appears to him as being extremely distressful and ridiculous.[2]
Chrysippus holds in the twelfth book of his Physics that there are two bases for judgment: sense-perception, knowledge, and preconception.[3] Furthermore, he says that preconception is a natural conception of universals.[4]
The philosopher Epicurus says[5] that preconception is as if it were a grasp, or correct opinion, or a conception that is a universal notion stored in us, i.e. a memory of what often appears to us from the external world. For instance, "such a thing is a man"; for as soon as the word "man" is pronounced its distinguishing feature is immediately conceived of due to preconceptions, since the senses serve as a guidance. Therefore, what primarily falls upon each name is something evident. And we would not have investigated what is an object of investigation if we had not known it first. For example, what is standing in front of me, is it a cow or a horse? For by means of preconception we must have known at some time the shape of horse or cow. We would not have given a name to anything if we had not first learned its distinguishing feature by means of preconception. Consequently, preconceptions are evident. And what is an object of opinion depends upon something prior and evident, by referring to which we ask: "how can we know if this thing is a man?"
They also call the opinion "supposition" [u(po/lhyis].