1911 Encyclopædia Britannica/Agrippa
AGRIPPA, a sceptical philosopher, whose date cannot be accurately determined. He must have lived later than Aenesidemus, who is generally said to have been a contemporary of Cicero. To him are ascribed the five tropes (πέντε τρόποι) which, according to Sextus Empiricus, summarize the attitude of the later ancient sceptics. The first trope emphasizes the disagreement of philosophers on all fundamental points; knowledge comes either from the senses or from reason. Some thinkers hold that nothing is known but the things of sense; others that the things of reason alone are known; and so on. It follows that the only wise course is to be content with an attitude of indifference, neither to affirm nor to deny. The second trope deals with the validity of proof; the proof of one so-called fact depends on another fact which itself needs demonstration, and so on ad infinitum. The third points out that the data of sense are relative to the sentient being, those of reason to the intelligent mind; that in different conditions things themselves are seen or thought to be different. Where, then, is the absolute criterion? Fourthly, if we examine things fairly, we see that in point of fact all knowledge depends on certain hypotheses, or facts taken for granted. Such knowledge is fundamentally hypothetical, and might well be accepted as such without the labour of a demonstration which is logically invalid. The fifth trope points out the impossibility of proving the sensible by the intelligible inasmuch as it remains to establish the intelligible in its turn by the sensible. Such a process is a vicious circle and has no logical validity. A comparison of these tropes with the ten tropes enumerated in the article Aenesidemus shows that scepticism has made an advance into the more abtruse questions of metaphysics. The first and the third include all the ideas expressed in the ten tropes, and the other three systematize the more profound difficulties which new thinkers had developed. Aenesidemus was content to attack the validity of sense-given knowledge; Agrippa goes further and impugns the possibility of all truth whatever. His reasons are those of modern scepticism, the reasons which by their very nature are not susceptible of disproof.
See Diogenes Laertius x. 88, and Zeller’s Greek Philosophy. Also the articles Scepticism; Aenesidemus.