The obscurity that involves all metaphysical subjects appears to me, in the same manner, peculiarly calculated to add to that class of excitements which arise from the thirst of knowledge. It is probable that man, while on earth, will never be able to attain complete satisfaction on these subjects; but this is by no means a reason that he should not engage in them. The darkness that surrounds these interesting topics of human curiosity may be intended to furnish endless motives to intellectual activity and exertion. The constant effort to dispel this darkness, even if it fail of success, invigorates and improves the thinking faculty. If the subjects of human inquiry were once exhausted, mind would probably stagnate; but the infinitely diversified forms and operations of nature, together with the endless food for speculation which metaphysical subjects offer, prevent the possibility that such a period should ever arrive.
It is by no means one of the wisest sayings of Solomon that ‘there is no new thing under the sun.’ On the contrary, it is probable that were the present system to continue for millions of years, continual additions would be making to the mass of human knowledge, and yet, perhaps, it may be a matter of doubt whether what may be called the capacity of mind be in any marked and decided manner increasing. A Socrates, a Plato, or an Aristotle, however confessedly inferior in knowledge to the philosophers of the present day, do not appear to have been much below them in intellectual capacity. Intellect rises from a speck, continues in vigour only for a certain period, and will not perhaps admit while on earth of above a certain number of impressions. These impressions may, indeed, be infinitely modified, and from these various modifications, added probably to a difference in the susceptibility of the original germs, arise the endless diversity of character that we see in the world; but reason and experience seem both to assure us that the capacity of individual minds does not increase in proportion to the mass of existing knowledge. (It is probable that no two grains of wheat are exactly alike. Soil undoubtedly makes the principal difference in the blades that spring up, but probably not all. It seems natural to suppose some sort of difference in the original germs that are afterwards awakened into thought, and the extraordinary difference of susceptibility in very young children seems to confirm the supposition.)