22. We must keep in mind the conceptions established by reality and the evidence provided by our senses, and to those we must refer all our opinions, otherwise all things in life will be full of confusion and doubt.

Alternate Translations: Bailey: We must consider both the real purpose and all the evidence of direct perception, to which we always refer the conclusions of opinion, otherwise all will be full of doubt and confusion. Strodach: It is necessary to take into account both the actual goal of life and the whole body of clear and distinct percepts to which we refer our judgments. If we fail to do this, everything will be in disorder and confusion.

Diogenes Laertius: In regard to the five senses, [Epicurus states] that the senses themselves are devoid of reason, and they are not capable of receiving any impressions from memory. For they are not by themselves the cause of any impression, and when they have received any impression from any external cause, they can add nothing to it, nor can they subtract anything from it. Moreover, they are not within the control of the other senses; for one sense cannot judge another, as all observations have an equal value, and their objects are not identical. In other words, one sensation cannot control another, since the effects of all of them influence us equally. Also, reason by itself cannot pronounce judgment on the senses; for … all reasoning rests on the senses for its foundation. Reality and the evidence provided by the senses establish the certainty of our faculties; for the impressions of sight and hearing are just as real, just as evident, as pain. It follows from these considerations that we should judge those things which are obscure by their analogy to those things which we perceive directly. In fact, every notion proceeds from the evidence provided by the senses, either directly, or as a result of some analogy, or proportion, or combination to that which we do perceive directly, reasoning always participating in these operations.

In regard to the preconceptions, Epicurus meant a sort of comprehension, or right opinion, or notion, or general idea which exists within us. In other words, a preconception is a kind of mental recollection of an external object that we experience before we perceive it. For instance, one example is the idea: “Man is a being of such and such Nature.” At the same moment that we utter the word man, we conceive the figure of a man, in virtue of a preconception which we owe to the preceding operations of the senses. [An anticipation is] therefore the first notion which each word awakens within us …. In fact, we could not seek for anything if we did not previously have some notion about it. To enable us to affirm that what we see at a distance is a horse or an ox, we must have some preconception in our minds which makes us acquainted with the form of a horse and an ox. We could not even give names to things, if we did not have a preliminary notion of what the things were. These preconceptions then furnish us with certainty. And with respect to judgments, their certainty depends on our referring them to some previous notion which has already been established to be certain. This is how we affirm or judge the answer to any question; for instance, “How do we know whether this thing is a man?”

Letter to Herodotus: First of all, Herodotus, one must determine with exactness the meaning and concept behind every word so that we are able to refer to that concept as an established standard as we pursue our research. Otherwise, the judgments that we reach will have no foundation, and we will go on studying to infinity without understanding, because we will be using words devoid of meaning. In fact, it is absolutely necessary that we grasp directly the fundamental concept which each word expresses, without need of reminder, if we are to have a standard on which to rest all our investigations. In order to do this we must keep all our investigations in accord with and reconciled to the evidence from our senses, especially in those matters in which our minds have grasped a clear view and reached a firm judgment. We must do this so we may identify that point in the examination where we find it necessary to reserve judgment as to the truth of a matter, which will occur when we do not have immediately perceptible to us sufficient evidence to form a clear determination.

Letter to Pythocles: The regular and periodic march of the heavenly phenomena has nothing in it that would surprise us if we would only pay attention to the analogous facts which take place here on earth under our own eyes. Above all things, let us beware against making a god interpose itself here, for we ought always to consider a god to be exempt from all toil and perfectly happy. Otherwise we shall find ourselves giving vain explanations to the heavenly phenomena, as has happened already to a crowd of philosophers. Because they do not recognize what is really possible and what is not, they have fallen into vain theories, supposing that for all phenomena there is but one single mode of production, and rejecting all other explanations which are also founded on probability. They have adopted the most unreasonable opinions because they failed to place in the forefront of the analysis the evidence of the senses, which ought always to serve as the first basis for explaining all phenomena.

Letter to Pythocles: The thunderbolt may be produced either by a violent condensation of the winds, or by their rapid motion and collisions. …. In short, one may give a number of explanations of the thunderbolt. Above all things we must always be on guard against fables, and fables will easily be avoided if one follows faithfully the phenomena that are observed directly in searching for the explanation of those things which are only perceived indirectly.

Lucretius De Rerum Natura Book I: But now to resume the thread of the design that I am weaving in verse: all nature then, as it exists by itself, is founded on two things: there are bodies and there is void in which these bodies are placed and through which they move about. For that material things exist is declared by the general acknowledgement of mankind. Unless, at the very first, our conviction of this is firmly grounded, there will be nothing to which we can appeal in regard to things that are only perceived indirectly, in order to prove anything by the reasoning of the mind. Then again, if room and space which we call void did not exist, bodies could not be placed anywhere nor move about at all to any side; as we have demonstrated to you already.

NewEpicurean Commentary: The ultimate goal of human life is to live a happy life here on this earth, in this reality, without being deceived that there is some other dimension or other standard for how we should live our lives. The key to determining the laws of Nature, and how they apply to us, is to refer all questions to our senses, and to make sure that all our opinions are consistent with reality as we sense and experience it. Applying any other standard other than a reasoned understanding of reality as experienced through our senses will lead to a life full of confusion and turmoil.