Isadore Twersky Harvard University
In contradistinction to the epistemology of classical philosophers or, more precisely, in a carefully premeditated expansion of the classical epistemological doctrine which recognized sense perception, primary premises (axioms), and scientific data (derivative knowledge) as sources of knowledge, the epistemology of medieval religious philosophers recognized not only these three but also tradition, true reliable tradition (received from the prophets or the wise men), as a supplementary source of knowledge. Maimonides writes in the Letter on Astrology - a document of particular importance for understanding the significance of science and philosophy in his thought and in which, as he himself emphasizes, statements elaborated elsewhere are reflected - as follows:
Know, my masters, that it is not proper for a man to accept as trustworthy anything other than one of these three things. The first is a thing for which there is a clear proof deriving from man’s reasoning such as arithmetic, geometry, and astronomy. The second is a thing that a man perceives through one of the five senses such as when he knows with certainty that this is red and this is black. The third is a thing that a man receives from the prophets or from the righteous.2
Maimonides then goes on to urge his readers clearly to identify each of these sources and not to blur them:
Every reasonable man ought to distinguish in his mind and thought all the things that he accepts as trustworthy and say: ‘This I accept as trustworthy because of tradition and this because of sense-perception and this on grounds of reason.’
Anyone who accepts as trustworthy anything that is not of these three species, of him it is said: ‘The simple believes everything.’ (Prov. 14:15).3
One consequence of this epistemological classification, emphasized by Maimonides, is that not everything written in a book is wisdom or truth; for a statement to be valid and trustworthy, it must be based on one or more of the sources of knowledge.4
