But the object of the scientific mind is not to observe and record all the phenomena presented to it in the continuity of consciousness. On the contrary, it neglects and rejects many; but always with a purpose, viz. that of ascertaining and describing, as precisely as possible, the conditions under which a given co-existence or sequence occurs (and therefore may be expected to recur) and without which it fails to occur. In other words, science assumes that everything has a cause, and that in accordance with the uniformity of nature what has happened once will happen again in the same circumstances; that a cause will, in the absence of counteracting causes, produce its effect. Without these assumptions science cannot treat of any subject: no department of knowledge can be dealt with scientifically if these assumptions are not admitted with regard to that department. On the other hand, if by the aid of these assumptions we are enabled to reduce any set of phenomena to law and order, our success is of itself sufficient ground for regarding the assumptions as warrantable and justifiable. For science, at any rate, the only question is whether as a matter of fact they do enable us to determine under what conditions given co-existences or sequences will ensue, or what conditions such a co-existence or sequence necessarily implies. With regard to human activity, mental and physical, it is plain matter of fact that such uniformities of sequence and co-existence not only can be but are demonstrated to prevail; and the extension of the scientific principle of cause and effect to the domain of human will and action is scientifically justified. The comparative sciences which deal with man and his works and words--archæology, anthropology, philology--are perpetually engaged in demonstrating, with fresh proofs every day, the uniformity of human nature: in similar circumstances men have always behaved in similar ways. To satisfy the same needs, they have manufactured similar instruments at similar stages of development: flint arrow-heads from Mexico or Japan resemble those taken from British barrows; the pottery of early Greece is hard to distinguish from that of Peru; the purpose of many stone implements of unknown antiquity has been discovered by a comparison of the use to which similar tools are put by savages still existing. That man's words, as well as his works, exhibit law, order, and uniformity in their growth, as well as in their phonetic decay, is shown by the science of comparative philology. That in the face of the same problems similar analogies have been used to produce similar solutions, is revealed by comparative mythology: the imagination, which might have seemed most free to throw off the trammels of law and of monotonous uniformity, falls in similar circumstances into very similar grooves.