George Berkeley  (1685-1753) Empricism, Nominalism, & Idealism
§ references refer to the numbered sections of Berkeley's Treatise Concerning the Principles of Human Knowledge 
  1. What I here make public . . . seemed to me to be evidently true, and not unuseful to be known, particularly to those who are tainted with scepticism, or want a demonstration of the existence and immateriality of God, or the natural immortality of the soul. (Preface)
  2. He must surely be either very weak, or very little acquainted with the sciences, who shall reject a truth that is capable of demonstration, for no other reason but because it is newly known and contrary to the prejudices of mankind. (Preface)

Introduction:
Denial of any mental power of abstraction & of the existence 
of abstract ideas. 

Berkeley argues against the existence of abstract ideas or universals.
LOCKE'S THEORY OF LANGUAGE
Words = meaningful sounds. Meanings = ideas associated with words.
Communication involves ideas in me causing me to utter the words that mean them which causes the same or similar ideas in you when you hear them. 
proper names "George" refers via associated concrete idea to George, a particular individual. 
general terms
"Man" refers via associated abstract idea to a whole set or class of individuals.
  1. And after this manner it is said we come to the abstract idea of man, or if you please humanity or human nature; wherein . . . there is included colour . . . but it can be neither white nor black, nor any particular colour; because there is no one particular color whereof all men partake. So likewise there is included stature, but then it is neither tall stature nor low stature nor yet middle stature, but something abstracted from all these. (§9)
  2. Whether others have this wonderful faculty of abstracting their ideas they best can tell: for myself I find indeed I have a faculty of imagining or representing to myself the ideas of those particular things I have perceived, and variously compounding and dividing them. . . . But then, whatever hand or eye I imagine, it must have some particular shape and colour. . . . I cannot by any effort of thought conceive the abstract idea [of an man] above described. (§10)
  3. I deny that I can . . . frame a general notion by abstracting from particulars in the manner aforesaid. (§10)
  4. But it seems that a word becomes general by being made the sign, not of an abstract general idea, but of several particular ideas. (§11)
  5. And as that particular line [drawn by the geometer] becomes general by being made a sign, so the name line, which taken absolutely is particular, by being a sign is made general. (§12)
  6. What more easy than for anyone to look a little into his own thoughts, and there try whether he has, or can attain to have, an idea that shall correspond with . . . the general idea of a triangle which is neither oblique, nor rectangle, nor equilateral, epicrural, nor scalene, but all and none of these at once? (§13) 
  7. [A] man may consider a figure merely as triangular, without attending to the particular qualities of the angles, or relations of the sides. So far he may abstract: but this will never prove that he can frame an abstract general inconsistent idea of a triangle. (§16)
  8. [I]t is not necessary. . . significant names which stand for ideas should, every time they are used, excite in the understanding the ideas they are made to stand for- in reading and discoursing, names being for the most part used as letters are in Algebra, in which, though a particular quantity be marked by each . . . it is not requisite that in every step each letter suggest to your thoughts that particular quantity it was appointed to stand for. (§19)
  9. To discern the agreements or disagreements that are between my ideas . . . there is nothing more requisite than an attentive perception of what passes in my own understanding. (§22)
  10. He who knows that words do not always stand for ideas will spare himself the labor of looking for ideas where none are to be had. (§24)

Part 1:
Critique of Materialism Defense of Immaterialism

"By matter therefore we are to understand an inert, senseless substance, in which extension, figure, and motion do actually subsist." (§9)

"[T]hough we give the materialists their external bodies, they by their own confession are never the nearer knowing how our ideas are produced; since they own themselves unable to comprehend in what manner body can act upon spirit, or how it is possible it should imprint any idea in the mind." (§19)

OBJECTION
There was a young man who said, "God Must think it exceedingly odd,
If he finds that this tree
continues to be,
when there's no one about in the Quad.
REPLY
Dear Sir: Your astonishment's odd:
I am always about in the Quad.
And that's why the tree
will continue to be,
Since observed by Yours faithfully, GOD.
  1. Thus, for example, a certain colour, taste, smell, figure, and consistence having been observed to go together, are accounted on distinct thing, signified by the name apple. (§1)
  2. This perceiving, active being is what I call mind, spirit, soul, or myself. By which words I do not denote any one of my ideas but a thing entirely distinct from them wherein they exist, or . . . whereby they are perceived; for the existence of an idea consists in being perceived. (§2)
  3. The table I write on, I say, exists, that is, I see and feel it; and if I were out of my study I should say it existed meaning that if I was in my study I might perceive it, or that some other spirit actually does perceive it. (§3)
  4. For as to what is said of the absolute existence of unthinking things without any relation to their being perceived, that seems perfectly unintelligible. Their esse is percipi, nor is it possible they should have any existence out of the minds of thinking things which perceive them. (§3)
  5. But my conceiving or imagining power does not extend beyond the possibility of real existence or perception. Hence as it is impossible for me to see or feel anything without an actual sensation of that thing, so is it impossible for me to conceive in my thoughts any sensible thing lor object distinct from the sensation or perception of it. (§5)
  6. Hence it is plain that the very notion of what is called matter, or corporeal substance, involves a contradiction in it. (§9)
  7. In short, let anyone consider those arguments which are thought manifestly to prove that colours and tastes exist only in the mind, and he shall find they may with equal force be brought to prove the same thing of extension, figure, and motion. (§10)
  8. In short, extension, figure, and motion, abstracted from all other qualities, are inconceivable. Where therefore, the other sensible qualities are, there must these be also, to wit in the mind and nowhere else. (§10)
  9. Now why may we not as well argue [as is for heat and cold] that figure and extension are not patterns or resemblances of qualities existing in matter, because to the same eye at different stations, or eyes of a different texture at the same station, they appear various, and cannot therefore be images of anything settled and determinate without the mind. (§14) 
  10. Hence it is evident the supposition of external bodies is not necessary for the producing of our ideas: since it is granted that they are produced sometimes, and might possibly be produced always, in the same order we see them in at present. (§19)
  11. But do you not yourself perceive or think of them all the while? This therefore . . . does not show that you can conceive it possible the objects of your thought may exist without the mind: to make this out, it is necessary that you conceive them existing unconceived or unthought of, which is a manifest repugnancy. (§23)
  12. All our ideas . . . are visibly inactive; there is nothing of power or agency included in them. (§24)
  13. [T]he cause of ideas is an incorporeal active substance or spirit. (§26)
  14. A spirit is one simple, undivided, active being: as it perceived ideas, it is called the understanding, and as it produces or otherwise operates about them, it is called the will. (§27)
  15. Such is the nature of spirit, or that which acts, that it cannot be of itself perceived but only by the effects which it produceth. (§27)
  16. The ideas of sense are more strong, lively, and distinct than those of the imagination; they have likewise a steadiness order and coherence and are not excited at random, as those which are the effects of human wills often are, but in a regular series, the admirable connexion whereof sufficiently testifies the wisdom and benevolence of its Author. (§30)
  17. Now the set rules or established methods wherein the Mind we depend on excites in us the ideas of sense, are called the laws of nature; and these we learn by experience, which teaches us that such and such ideas are attended with such and such other ideas, in the ordinary course of things.. (§30)
  18. That the things I see with my eyes and touch with my hands do exist, really exist, I make not the least question. The only thing whose existence we deny is that which philosophers call Matter or corporeal substance. (§35)
  19. [I]t will be objected, that from the foregoing principles . . . things are every moment annihilated and created anew. (§45)
  20. [T]he matter philosophers contend for is an incomprehensible somewhat, which hath none of those particular qualities whereby the bodies falling under our senses are distinguished one from another. (§47)
  21. We may not conclude that they have no existence, except only while they are perceived by us, since there may be some other spirit that perceives them, though we do not. (§48) 
  22.  [T]he absolute existence of unthinking things are words without a meaning, or which include a contradiction. (§24)
  23. There is a rerum natura, and the distinction between realities and chimeras retains its full force. . . . [B]ut then they both equally exist in the mind, and in that sense they are alike ideas. (§34)

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