Another question has been asked of Berkeley which goes deeper. If to be is to be perceived, what existence has a tree in the forest that no one has ever perceived. What existence have past events that are forgotten? Berkeley has considered this objection and has answered it. When he says that existence depends upon perception, he does not mean merely my own perception. Berkeley is not what in philosophy is called a solipsist (_solus_ and _ipse_), _i. e._ one who believes that nothing exists but himself and his modifications. A thing may have existence in the mind of some one else. If the thing has never been perceived by any human being, it is perceived, if the thing exists, by the mind of God. The modern scientist assumes the existence of matter in the whole universe. Berkeley assumes the existence of a perceiving God. One is the materialistic and the other the religious explanation of the universe. =The Life and Writings of David Hume[44]= (1711–1776). Hume’s life bears some marks of external resemblance to Berkeley’s. After periods of training that differed very greatly in point of discipline, but were almost the same in point of time, both produced, at about the age of twenty-five, their most important philosophical works. Both turned from philosophy to other pursuits――Berkeley to missionary work at the age of thirty-six, and Hume to politics at the age of forty-one. There the resemblance between the two men ceases; for they were antipodal by nature, and animated by different purposes. The enthusiastic nature of Berkeley is in marked contrast with the unimpassioned nature of the Scot. Hume was unimaginative to the last. He was unimpressed by the legends of the border where he lived; he had no love for nature and no appreciation of art. “While Hume’s intellect was imperial, his sympathies were provincial.” Berkeley’s sympathies were imperial and his intellect was in their service. Hume was a man of kindly disposition and of moderate temper, yet he was vain, and interested above everything else in his own reputation. No object seemed worth while to him, unless it made for the improvement of his talents in literature. The failure of the _Treatise_ was a blow from which he never recovered. Always afterward he had an eye to popularity, and this is important in making up our judgment about him. All his works after the _Treatise_ were written to please his readers and for personal success. Locke the Englishman, Berkeley the Irishman, and Hume the Scotchman came from the same middle class of society, had university training, were engaged in public service, and are to be classed in the same empirical school of philosophy. But they were personally very different kinds of men, and were types, although perhaps not representatives, of their nationalities.