2. But, in truth, we must acknowledge, before we proceed with this subject, that, speaking with strictness, an _Art of Discovery_ is not possible;--that we can give no Rules for the pursuit of truth which shall be universally and peremptorily applicable;--and that the helps which we can offer to the inquirer in such cases are limited and precarious. Still, we trust it will be found that aids may be pointed out which are neither worthless nor uninstructive. The mere classification of examples of successful inquiry, to which our rules give occasion, is full of interest for the philosophical speculator. And if our maxims direct the discoverer to no operations which might not have occurred to his mind of themselves, they may still concentrate our attention on that which is most important and characteristic in these operations, and may direct us to the best mode of insuring their success. I shall, therefore, attempt to resolve the Process of Discovery into its parts, and to give an account as distinct as may be of Rules and Methods which belong to each portion of the process. 3. In Book II. we considered the three main parts of the process by which science is constructed: namely, the Decomposition and Observation of Complex Facts; the Explication of our Ideal Conceptions; and the Colligation of Elementary Facts by means of those Conceptions. The first and last of {143} these three steps are capable of receiving additional accuracy by peculiar processes. They may further the advance of science in a more effectual manner, when directed by special technical _Methods_, of which in the present Book we must give a brief view. In this more technical form, the observation of facts involves the _Measurement of Phenomena_; and the Colligation of Facts includes all arts and rules by which the process of Induction can be assisted. Hence we shall have here to consider _Methods of Observation_, and _Methods of Induction_, using these phrases in the widest sense. The second of the three steps above mentioned, the Explication of our Conceptions, does not admit of being much assisted by methods, although something may be done by Education and Discussion.