 There are five virtues of thought: technê, epistêmê, phronêsis, sophia, and nous (1139b15). Various translations have been offered for each of these terms. Most often, technê is translated as craft or art. While epistêmê is generally rendered as knowledge, in this context, where it is used in its precise sense, it is sometimes translated as scientific knowledge. However, one must not confuse this usage with our contemporary understanding of science, which includes experimentation. Conducting experiments to confirm hypotheses is a much later development. Rather, translating epistêmê as scientific knowledge is a way of emphasizing its certainty. In any event, as soon as Aristotle introduces these five terms, he turns to the distinction between the first two virtues. First he defines epistêmê, as he says, in its accurate sense and leaving aside its analogous uses. Scientific knowledge is distinguished by its objects, which do not admit of being otherwise; these objects are eternal and exist of necessity. More precisely, scientific knowledge comprises demonstration, starting from first principles; the latter must also be known, although they are not known by demonstration (1139b15–30). The full account of epistêmê in the strict sense is found in Posterior Analytics, where Aristotle says that we think we know something without qualification (epistasthai…haplôs) when we think we know (gignôskein) the cause by which the thing is, that it is the cause of the thing, and that this cannot be otherwise (71b10–15). As though to emphasize the necessity of what is known, he most frequently uses geometry as an example of epistêmê. In this regard, it should be pointed out that Aristotle uses the notion of cause (aitia) in a broader sense than it usually has in contemporary thought. Thus, understanding how the geometrical axioms lead to a theorem that right triangles have a certain property would be an instance, for Aristotle, of understanding the cause of the proven property of the right triangle.