[W]e can ascend to remote periods by a chain of causes, but in none can we ascend to a 'beginning' of the chain.

The Catastrophist constructs theories, the Uniformitarian Demolishes them.

There are, in the Palætiological Sciences, two antagonist doctrines: 'Catastrophes' and 'Uniformity'. The doctrine of a 'uniform course of nature' is tenable only when we extend the notion of uniformity so far that it shall include catastrophes.

The Palætiological Sciences depend upon the Idea of Cause; but the leading conception which they involve is that of 'historical cause', not mechanical cause.

The idea of living beings as subject to 'disease' includes a recognition of a Final Cause in organization; for disease is a state in which the vital forces do not attain their 'proper ends'.

The assumption of a Final Cause in the structure of each part of animals and plants is as inevitable as the assumption of an Efficient Cause for every event. The maxim that in organized bodies nothing is 'in vain', is as necessarily true as the maxim that nothing happens 'by chance'.

In 'voluntary' motions, Sensations produce Actions, and the connexion is made by means of Ideas: in 'reflected' motions, the connexion neither seems to be nor is made by means of Ideas: in 'instinctive' motions, the connexion is such as requires Ideas, but we cannot believe the Ideas to exist.

Mechanical, chemical, and vital Forces form an ascending progression, each including the preceding. Chemical Affinity includes in its nature Mechanical Force, and may often be practically resolved into Mechanical Force. (Thus the ingredients of gunpowder, liberated from their chemical union, exert great mechanical Force : a galvanic battery acting by chemical process does the like.) Vital Forces include in their nature both chemical Affinities and mechanical Forces: for Vital Powers produce both chemical changes, (digestion,) and motions which imply considerable mechanical force, (as the motion of the sap and of the blood.)

Life is a System of Vital Forces ; and the conception of such Forces involves a peculiar Fundamental Idea.

It has been proved by the biological speculations of past time, that organic Life cannot rightly be resolved into mechanical or chemical forces, or the operation of a vital fluid, or of a soul.