Now with regard to this system, whatever we may think of the solidity of the foundation, the superstructure is as light and elegant as possible. There is a peculiar character in the metaphysical writings of Berkeley which is to be found no where else. With all the closeness and subtilty of the deepest reflection, they combine the ease and vivacity of a common essay: so that the most violent paradoxes and elaborate distinctions are rendered familiar by the simplicity of the style. His writings show that he had thought with the utmost intensity on almost every subject, yet he has the same careless freedom of manner as if he had never thought at all. He is never entangled in the labyrinth of his own thoughts, and the buoyancy of his spirit surmounts every objection with a singular felicity, as if his mind had wings. It is perhaps worth remarking that the ‘Principles of Human Knowledge’ were published in 1710, at a time when the author was only five-and-twenty, as was the ‘Essay on Vision,’ the greatest by far of all his works, and the most complete example of elaborate analytical reasoning and particular induction joined together that perhaps ever existed. It is also generally free from that air of paradox and fanciful hypothesis which runs through his other writings.[7] I mention this the more because I believe that the greatest efforts of intellect have almost always been made while the passions are in their greatest vigour, and before hope loses its hold on the heart, and is the elastic spring which animates all our thoughts. On the reasoning I have just quoted I will make one or two remarks without pretending to enter into the real difficulties of the question. First, it seems to me that the argument against the existence of the secondary qualities, drawn from the various effects produced by them on different minds or in different circumstances, which Hume mentions as the only solid one, and which Berkeley thinks more doubtful, is no argument at all. That an object at a distance, for example, does not look like the same object near is in consequence of the interposition of the air, which gives it a different hue; the logical inference merely is that one object has not the same sensible qualities as another, or as Berkeley has remarked, since the effect depends upon the combination and reaction of a number of things that we do not know what the true or natural qualities of each object are.