No search into the relations of matter and motion can ever affect our consciousness of causality. We cannot be conscious of our own being without being simultaneously conscious that whatever begins to be, must have a cause, a reason, for its being. The very validity of our mental acts is imperilled, if the congruity of the principle of causality be doubted. Permit an illustration: a minute and beautiful crystal of unknown nature is before us. By a mental necessity we know—we cannot free ourselves from the conviction—that this crystal occupied a measurable time to become a crystal, and that being such, it occupies a measurable portion of space. May we rely on this fundamental act of mind? Is it truth? If not, there is not a mental act that ever was, or ever can be, veritable. But if it be true, then, since for man to produce a physical effect involves (1) the consciousness of _power_ to do it, and (2) the volitional exercise of that power; and since the human mind is absolutely without a trace of knowledge of any other way in which power can be exercised, in earth or heaven; is not the insistence of reason that there must be a cause for cosmic phenomena, a mental act of the _same order_ as that which insists on time and space as inseverable factors in the origin and existence of a crystal? Causality in its mere mechanical relations may be considered for convenience, and translated as, ‘mechanical law:’ contemplated in its relation to a living organism, we may render it by such an expression as a ‘law of life’. But carry causality to its spring, trace it back to consciousness and thought, and it admits of no disguise; it is power, it is volition; there is no halting in its phrase; it is, ‘I can,’ ‘I will.’ Herbert Spencer himself affirms, ‘The force by which we ourselves produce changes, and which serves to symbolize the causes of changes in general, is the final disclosure of analysis.’[3] ‘I can,’ ‘I am able,’ is a knowledge that emerges within us simultaneously with ‘I am.’ It involves a consciousness of power, which is the essence of causality. We possess it, in precisely the same way as we possess ourselves, or our thoughts. Our knowledge of power is not even derived from effort or resistance. We know as clearly what we mean by ‘I am able,’ as we do when we affirm ‘I am here.’ Being able, and _knowing_ we are able, are absolutely different. A telephone is mechanically able to transmit vocal sounds and language. But how different to man, who is not only able, but knows that he is able. This knowledge of our power to act is the immutable foundation of our belief in causation. [Footnote 3: _First Principles_, §50, pp. 169, 170.]