Diogenes Laërtius

...functions exist in the nature of things themselves, or exist truly and in reality. Indeed, our seeing and hearing is something that really exists, just as much as feeling pain. There is no difference between saying something is true or saying it exists.

From these things it follows that we must draw a conjecture from those things appearing to the Senses toward those things that are hidden from us. All mental notions have their origin from the Senses, either by incidence original: "incidentiam". This refers to the direct impact of an object's physical film or "eidolon" upon the sense organs. (namely, when things fall directly and by themselves into the sense, like a specific man seen face to face) or by a certain proportion of things perceived by sense (like when a Giant is conceived by enlarging, or a Pygmy by shrinking, while keeping the same proportion of parts observed in a man of normal size) or by similarity (like when we imagine an unseen city based on one we have seen) or finally by composition (like when we imagine a Hippocentaur A mythical creature with the upper body of a human and the lower body of a horse. from seeing a horse and a man) with reasoning also contributing something to this.

I pass over the fact that the visions of those who are delirious or dreaming are also considered true because they exist in reality. It is established that they exist in reality because they move the faculty of sense. Clearly, that which does not exist can move nothing at all.

Then, by the name of Anticipation or Preconception, they understand a mental grasp or a certain fitting opinion, or if you prefer, an understanding or universal notion fixed in the mind, existing as a memory,

The following Greek text is a passage from Diogenes Laertius, Book 10, Section 31 to 34, which the author is translating into Latin and discussing in the surrounding text.

...subsisting, confirms the truth of the senses. Our seeing and hearing subsists, just like feeling pain. Therefore, there is no difference between something being true or subsisting.

5 Hence, one must also infer the unknown from the apparent things. For all thoughts have come from the senses by incidence, analogy, similarity, and composition, with reasoning also contributing something.

10 The visions of madmen and those in dreams are true, for they move the senses; but that which does not exist does not move anything.

They say anticipation original: "πρόληψιν" (prolepsis). A foundational concept in Epicureanism referring to a "preconception" or innate-like general idea formed from repeated sensory experiences. is like a mental grasp, or a right opinion, or a concept, or a universal thought stored away, that is, a memory of what has often appeared from the outside, such as "Man is such a thing." For as soon as "man" is spoken, immediately the form is understood by anticipation, with the senses leading the way. Therefore, the primary thing underlying every name is clear. We would not have searched for what we seek unless we had known it before. For instance, "Is that thing standing far off a horse or an ox?" For one must have known the form of a horse and an ox by anticipation at some time. Nor would we have named anything unless we had first learned its form by anticipation. Anticipations are therefore clear. And the object of opinion depends on something previously clear, to which we refer when we speak. For instance, "How do we know if this is a man?" They also call opinion original: "δόξαν" (doxa). In this system, opinion is the step where error can occur, unlike raw sensation. "supposition." They say it is both true and false, because of the addition or subtraction of something, or the presence or absence of witness...

...or a record of that thing which has appeared frequently from the outside. An example is the idea, or form, and that species to which we look when we say to ourselves, "Such a thing is a Man." Indeed, as soon as we hear this word, "Man," spoken, the image of a man is immediately understood according to the anticipation shaped in the soul by previous Senses. For this reason, the thing that is first and chiefly grasped by the mind when a word is spoken is something clear. We would not seek something if we did not already have a preconception of it. For example, when we ask: is that which appears far away a horse or an ox? One must have seen and known the form of a horse and ox by anticipation at some point. Indeed, otherwise, we would not even name a thing unless we held some image of it known by anticipation. In this way, anticipations are evident things. Furthermore, when we form an opinion on something, it depends on some previously evident thing. We attend to this evident thing, referring our thought to it, when we declare that this thing is such or is not. An example is the Preconception we have of a man. We attend to it as something evident when it is asked: "Is this thing seen a man or not?" We then judge it to be a man or not. They call Opinion by another name, Appraisal or Judgment. They teach that opinion (unlike Sense) is capable of being true or false, insofar as it adds or subtracts something from what appears, and the evidence itself supports it or opposes it.