We further saw that the only uniformity science requires of the actual course of nature is uniformity sufficiently close to enable us, for our special purposes, to neglect the individual deviations, and that the principle of Uniformity itself is not a logical axiom but a practical postulate, expressing the condition necessary for the successful formulation of rules for practical intervention in the course of events. Finally, while we saw that we have no _a priori_ logical warrant for the assumption that such rules can be formulated for all departments of the physical order, we are bound on methodological grounds to assume that they can, unless we have special positive reasons for believing the contrary. Thus the universality of a postulate of uniformity does not mean that it is universally _true_, but that it has universally to be made wherever we have an interest in attempting the formulation of general rules. § 5. (4) _The Conception of the Physical Order as a Mechanism._ The conception of nature as rigidly conformable to general laws, finds its completest expression in the view of the whole physical order as a complicated _mechanism_. It is not easy to say just how much is always implied when we hear of a “purely mechanical” theory of the world or of physical processes. Sometimes all that is meant is that the theory in question treats the principle of rigid uniformity according to general laws as an ultimate axiom. Sometimes, again, a “mechanical view” of the world is taken to mean, in a narrower sense, one which regards all the chemical, electrical, and other processes of the physical order as merely complicated cases of change of configuration in a system of mass particles. In this narrower sense the “mechanical” theory of the physical world is another name for the somewhat crude form of realist Metaphysics according to which nothing exists but moving masses, everything in the form of secondary qualities being a subjective illusion. Both the wider and the narrower form of the mechanical view agree in treating the processes of physical nature as unintelligent and unconscious, and regarding them as completely determined by antecedent conditions, without reference to any end or purpose which they effect. The theory owes the epithet “mechanical” to the analogy which is then supposed to subsist between the physical order and the various machines of human construction, in which the various constituent parts similarly execute movements determined by relation to the remaining parts, and not by any consciousness of an end to be attained.[138]