Alongside the philosophic programme which Deleuze inherited as his own, we can also turn our attention to his philosophical preferences, his philosophical tastes. Deleuze's name is frequently discussed alongside that of Spinoza, and it is this seventeenth-century philosopher that expresses Deleuze's preferences with unrivalled clarity. This is because Spinoza is the philosopher of the ‘synthetic method’.

Generally speaking, the synthetic method constitutes an oppositional pair with the analytic method, whose chief exponent is Descartes. Without going into too much detail, both of these methods are concerned with the way in which a philosophical theory is set forth. The analytic method begins from the facts which are given, that is the effect, which it proceeds to analyse in meticulous detail to arrive at the cause. In contradistinction, the synthetic method begins from the first principle whence all things originate, in other words it moves from cause to effect. For Descartes it is the analytic method which is the proper pathway to truth. Deleuze, on the other hand sees in Spinoza's Ethics the culmination of the synthetic method as the pathway to truth (EPS, 159–60/144–7).

On a first approach, it may seem that the two methods only traverse the same path, just in opposite directions. However, rotational symmetry is broken when we consider that the synthetic method has a difficulty peculiar to it. It wants to have the one principle as its point of departure, but this principle is not something pre-given. How then are we to get there? Precisely by passing through a sort of analytic procedure. And this principle having been attained, the very procedure thereto is subsumed as the preparatory part of the synthetic method itself. In other words, a more exacting definition of the synthetic method would have to be given in terms of the change of direction from the ‘regress to the principle’ to the ‘progress from the principle’. It is in this sense that the synthetic method is not a simple mirror image of the analytic. ‘The two types of systems [synthetic and analytic] can thus be distinguished structurally, that is to say, more profoundly than just by a simple opposition’ (‘Gueroult's General Method for Spinoza’, in DI, 147/203).