A still more cogent argument in favour of the strictly speculative treatment of the problem is this. The problem of perception may be said to be a _reversed_ problem. What are the means in every other problem, are in _this_ problem the end--and what is the end in every other problem, is in this problem the means. In every other problem the solution of the problem is the end desiderated: the means are the thinking requisite for its solution. But here the case is inverted. In _our_ problem the desiderated solution is the means, the end is the development, or, we should rather say, the creation of speculative thought--a kind of thought different altogether from ordinary popular thinking. "Oh! then," some one will perhaps exclaim, "after all, the whole question about perception resolves it into a _mere gymnastic_ of the mind." Good sir--do you know what you are saying? Do _you_ think that the mind itself is any thing except a mere gymnastic of the mind. If you do--you are most deplorably mistaken. Most assuredly the mind only _is_ what the mind _does_. The existence of thought is the exercise of thought. Now if this be true, there is the strongest possible reason for treating the problem after a purely speculative fashion. The problem and its desired solution--these are only the means which enable a new species of thinking, (and that the very highest) viz. speculative thinking, to deploy into existence. This deployment is the end. But how can this end be attained if we check the speculative evolution in its first movements, by throwing ourselves into the arms of the _apparently_ Common Sense convictions of Dr Reid? We use the word "apparently," because, in reference to this problem, the apparently Common Sense convictions of Dr Reid, are not the _really_ Common Sense convictions of mankind. These latter can only be got at through the severest discipline of speculation.