Getting away from Philodemus On Signs for a moment, I’ve been looking at The Hellenistic Philosophers by Long and Sedley for original quotes from Epicurus regarding signs and methods of inference. I also had a look at a cluster of Principle Doctrines that are relevant (PD 22 & 23 are from Nate’s compilation, with thanks).
PD22 We must take into account both the underlying purpose and all the evidence of clear perception, to which we refer our opinions. Otherwise, everything will be filled with confusion and indecision. O'Connor (1993)
PD23 If you resist all the senses, you will not even have anything left to which you can refer, or by which you may be able to judge of the falsehood of the senses which you condemn. Yonge (1853)
PD24 (1) If you are going to reject any sensation absolutely, and not distinguish opinions reliant on evidence yet awaited from what is already present through sensation, through feelings, and through every focusing of thought into an impression, you will confound all your other sensations with empty opinion and consequently reject the criterion in its entirety. (2) And if you are going to treat as established both all the evidence yet awaited in your conjectural conceptions, and that which has failed to <earn> attestation, you will not exclude falsehood, so that you will have removed all debate and all discrimination between correct and incorrect. Long and Sedley (1987, p. 135-6, kindle version)
Letter to Herodotus 37-38 (1) First, then, Herodotus, we must grasp the things which underlie words, so that we may have them as a reference point against which to judge matters of opinion, inquiry and puzzlement, and not have everything undiscriminated for ourselves as we attempt infinite chains of proofs, or have words which are empty. For the primary concept corresponding to each word must be seen and need no additional proof, if we are going to have a reference point for matters of inquiry, puzzlement and opinion. (2) Second, we should observe everything in the light of our sensations, and in general in the light of our present focusings whether of thought or of any of our discriminatory faculties, and likewise also in the light of the feelings which exist in us, in order to have a basis for sign-inferences about evidence yet awaited and about the non-evident. Long and Sedley (1987, p. 136, kindle version)