25. If on each occasion, instead of referring your actions to the end of nature, you turn to some other nearer standard when you are making a choice or an avoidance, your actions will not be consistent with your principles.

Lucretius De Rerum Natura Book IV: Many are the marvels … we see which seek to shake the credit of the senses. But such efforts are quite in vain, since the greatest part of these cases deceive us on account of the opinions which we add ourselves, taking things as seen which have not been seen by the senses. For nothing is harder than to separate those facts that are clearly true from those that are doubtful which the mind adds itself.

Diogenes Laertius: The Epicureans refer to ‘opinion’ as supposition, and say that it is at times true, and at times false. An opinion which is supported by evidence, and is not contradicted by other evidence is true. An opinion which is not supported by evidence, and is contradicted by other evidence, is false. On this account they have introduced the expression of “waiting,” such as when, before pronouncing that a thing seen is a tower, we must wait until we approach it, and learn what it looks like when we are nearby.

NewEpicurean Commentary: If you allow yourself to think that speculations which are not grounded in reality (such as speculations about the heavens or about infinity, subjects which you do not have the ability to verify) are of equal authority with deductive reasoning grounded in direct evidence (such as observations about things close at hand that you know to be true by experience) you will surely fall into error, because you will be confusing what is speculative with what is certain.