In order that the description substituted by our intellectual activity for the facts which we want to describe may convey these facts it is necessary to perform an act of synthesis on the description analogous to the act of perception which originally created the fact itself out of mere matter. The words used in a description should be to the hearer what mere matter is to the perceiver: in order that matter may be perceived an act of synthesis must be performed by which the matter is turned into fact in duration: similarly in order to gather what a description of a fact means the hearer must take the general terms which are employed not as being distinct and mutually exclusive but as modifying one another and interpenetrating in the way in which the “parts” of a process of creative duration interpenetrate. In the same way by understanding the terms employed synthetically and not intellectually we can use a description to recall any fact which we have once known directly. Thus our knowledge advances by alternate acts of direct acquaintance and analysis. Philosophy must start from a fresh effort of acquaintance creating, if possible, a fact wider and fuller than the facts which we are content to know for the purposes of everyday life. But analysis is essential if the fact thus directly known is to be conveyed to others and recalled. By analysis the philosopher fixes this wider field in order that he may communicate and recall it. Starting later from the description of some fact obtained by a previous effort of acquaintance, or from several facts obtained at different times, and also from the facts described by others, and using all these descriptions as material, it may be possible, by a fresh effort, to perform acts of acquaintance, (or synthesis) embracing ever wider and wider fields of knowledge. This, according to Bergson, is the way in which philosophical knowledge should be built up, facts, obtained by acts of acquaintance, being translated into descriptions only that these descriptions may again be further synthesised so directing our attention to more and more comprehensive facts. Inevitably, of course, these facts themselves, being less than all the stream of creative duration to which they belong, will be abstractions, if taken apart from that whole stream, and so distorted. This flaw in what we know even by direct acquaintance can never be wholly remedied short of our succeeding in becoming acquainted with the whole of duration. It is something, however, to be aware of the flaw, even if we cannot wholly remedy it, and the wider the acquaintance the less is the imperfection in the fact known.