 The theory of demonstration represents for Avicenna not only an essential part of logic but its true culmination. Its central problems are the identification of (i) the conditions under which certainty (yaqīn) may be attained in making assertions within the context of a scientific discipline and the identification of (ii) the conditions under which completeness, relevance, and accuracy may be achieved in the process of concept formation that leads to definitions. This determines in turn the nature of the principles assumed in each science for the derivation of its own theorems, the way in which boundaries between disciplines are drawn, and more generally the overall architecture of scientific knowledge.