George Berkeley, the metaphysician, was born on March 12, 1685, near Thomastown, Kilkenny, the son of a collector of revenue. He entered Trinity College, Dublin, at the age of fifteen, and was admitted Fellow in 1707. In that year he published two mathematical essays; two years later, his "Theory of Vision," and in 1710 his "Principles of Human Knowledge." In 1713, in London, where he had published further philosophical papers, he formed the acquaintance of Steele, Swift, and Pope. After travels in Europe he became chaplain to the Lord-Lieutenant of Ireland in 1721, and a few years after emigrated to Newport, Rhode Island, with a view to the establishment of a college in Bermuda for the education of Indians. This scheme fell through, because of the failure of the promised government support. Berkeley returned to London, and in 1734, by desire of Queen Caroline, was consecrated Bishop of Cloyne, in Ireland. Here he lived until 1752, but spent his last months in retirement at Oxford, where he died on January 14, 1753. Berkeley's "Principles of Human Knowledge" is one of the most eminent of that sequence of metaphysical systems which, beginning with Descartes, constitutes what is known as modern philosophy. _I.--THE ANALYSIS OF PERCEPTION_ It is evident to anyone who takes a survey of the objects of human knowledge that they are either ideas actually imprinted on the senses, or else such as are perceived by attending to the passions and operations of the mind; or, lastly, ideas formed by help of memory and imagination, either compounding, dividing, or representing those originally perceived in the aforesaid ways. By sight, touch, and other senses, I receive various sensations; and any group of sensations, frequently accompanying one another, come to be known as one thing. Thus a certain colour, taste, smell, figure, and consistence, having been observed to go together, are accounted one distinct thing--for instance, an apple. But, besides this endless variety of objects of knowledge, there is also the "mind," "spirit," "soul," or "myself," which perceives them. Neither our thoughts or imaginations, nor even the sensations which compose the objects of perception, can exist otherwise than in a mind perceiving them. It is impossible that objects should have any existence out of the minds for which they exist; to conceive them as existing unperceived is a mere abstraction. Whence it follows that there is no other substance but spirit, or that which perceives.