The laws which for us constitute the order of the world are of two kinds. Some are established by the positive method in each order of phenomena separately considered; the astronomical laws, physical laws, chemical laws, etc. They belong to the domain of science properly so-called. The others are apprehended when the mind leaves the special point of view of science, and places itself at the universal point of view of philosophy. They are found again in the different orders of phenomena, whose relations they express without compromising their respective independence. They represent them severally connected, or, according to Comte’s expression, as convergent. Comte calls these last _encyclopædic_ laws. They tend to realise the unity which the mind claims, not in pursuing the chimerical reduction of all laws to a supreme law, but in showing that the systems of irreducible laws are nevertheless harmonious among themselves. Generally speaking, these laws have been known for a long time, but only as special laws of such and such an order of phenomena. It belongs to positive philosophy to give them their encyclopædic character, that is to say, to make them universal. For instance, d’Alembert’s principle is known in mechanics as a law which connects questions of movement with questions of equilibrium. Philosophy finds a similar law in biology: (physiological questions are correlated to anatomical questions); and also in sociology (“progress is the development of order”). It then formulates the encyclopædic law which generalises these three laws, that is, the principle of the conditions of existence. Similarly the three great laws of mechanics, known under the name of the laws of Kepler, of Galileo and of Newton, must be universalised and become encyclopædic for they are applicable to all the orders of phenomena.[80] The law of Kepler, in the first place, expresses the spontaneous tendency of all natural phenomena to persevere indefinitely in their state, if no disturbing influence supervenes; a tendency whence are derived inertia in mechanics, habit in living bodies, and the conservative instinct in societies. The law of Galileo which reconciles every common movement with the various particular movements, applies to all the organic and inorganic phenomena. For, in any system, we can always ascertain the independence of the several active or passive mutual relations with regard to any action which is exactly common to the various parts, whatever may be their kind and degree. Finally the universal character of Newton’s law (reaction is equal to action), is evident at first sight. It is accidentally, not essentially, that these laws have at first been mechanical laws. They could have been equally attained by the study of biological or social phenomena. If the science of mechanics was the first to formulate them it is because it has for its object the less complicated phenomena.