William Whewell

[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 …

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 …

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 …

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.

The basis of all Natural Systems of Classification is the Idea of Natural Affinity. The Principle which this Idea involves is this:—Natural arrangements, obtained from 'different' sets of characters, must 'coincide' with each other.

The 'Diagnosis', or Scheme of the Characters, comes, in the order of philosophy, after the Classification. The characters do not 'make' the classes, they only enable us to 'recognize' them. The Diagnosis is an Artificial Key to a Natural …

A Natural Group is steadily fixed, though not precisely limited; it is given in position, though not circumscribed; it is determined, not by a boundary without, but by a central point within; —not by what it strictly excludes, but by what …

Natural Groups are best described, not by any definition which marks their boundaries, but by a 'Type' which marks their centre. The Type of any natural group is an example which possesses in a marked degree all the leading characters of …

A 'Natural System' is one which attempts to make 'all' the divisions natural, the widest as well as the narrowest; and therefore applies 'no' characters 'peremptorily'.

An 'Artificial System' is one in which the 'smaller' groups (the Genera) are 'natural'; and in which the 'wider' divisions (Classes, Orders) are constructed by the 'peremptory' application of selected Characters

The Plan of the System, may aim at a Natural or an Artificial System. But no classes can be absolutely artificial, for if they were, no assertions could be made concerning them.

The " Five Words," 'genus', 'species', 'difference', 'property', 'accident', were used by the Aristotelians, in order to express the subordination of kinds, and to describe the nature of definitions and propositions. In modern times, these …

A whale is not a fish in natural history, but it is a fish in commerce and law. A plea that human laws which mention fish do not apply to whales, would be rejected at once by an intelligent judge.

We collect individuals into 'kinds' by applying to them the Idea of Likeness.

All hypotheses respecting the manner in which the elements of inorganic bodies are arranged in space, must be constructed with regard to the general facts of crystallization.

The governing principles of chemical affinity are, that it is elective ; that it is definite ; that it determines the properties of the compound; and that analysis is possible.

Attractions take place between bodies, affinities between the particles of a body. The former may be compared to the alliances of states, the latter to the ties of family.

Coexistent polarities are fundamentally identical.

The solution is, that we do not see the image on the retina at all, we only see by means of it.