Since my post on Berkeley's metaphysics generated so much interesting discussion, I thought I would write a post on Berkeley's taxonomy of ideas. A particularly interesting (to me) aspect of this discussion is the way it plays into his critique of John Locke's theory of abstraction. Also of interest is the way this view (may have) influenced Immanuel Kant's epistemology of metaphysics. I'll skip lightly over that last one, because I don't understand Kant very well (who does?), but I re-read the Prolegomena recently and was thinking about this, so I'll float a few ideas by toward the end of this post and perhaps people who understand Kant better than I do will pick up on them.
The first point that must be made here is just what an 'idea' is. Berkeley is a sort of revisionist Lockean (one might say that Berkeley is a Lockean the way Arminius is a Calvinist) and, as such, essentially every one of his views is set up in either agreement or opposition with Locke's views. Berkeley would have had Locke's Essay Concerning Human Understanding as a logic textbook when he worked on his B.A. degree at Trinity College, Dublin. The point of this digression is that Berkeley uses words such as 'matter,' 'idea,' and 'abstraction' according to Locke's definitions. This is, in my oppinion, sometimes a problem for him: for instance, he shocks people by claiming that he doesn't believe in matter or the capacity of abstraction, but he actually means that he doesn't believe in John Locke's theories of matter and abstraction. According to modern, everyday usage, Berkeley believes in both.
Returning to the point, Locke defines the word 'idea' at Essay 2.1.1 as "the object of thinking" and goes on to divide ideas into 'simple' and 'complex.' Simple ideas are the basic, fundamental constructs or sensations - for instance, a particular shade of the color red - which cannot be broken down into constituent ideas, and out of which all of our complex ideas are composed (see Essay 2.2). Thus complex ideas are collections of simple ideas which are united with one another in a single "object of thinking," as in the case of the red water bottle on my desk. Locke's principle point here is empiricism: it is his contention that all of our complex ideas are built up from simple ideas, and we get simple ideas from sense perception.
All of this Berkeley accepts. There is much more that Locke says about ideas, and it is certain that all of it heavily influenced Berkeley, and certainly some of what I will now say about Berkeley is only repeat of distinctions made by Locke. Nevertheless, there are important differences, especially, as has been said, with regard to abstraction.
What I am calling 'Berkeley's Taxonomy of Ideas' seems to have acheived its full development in the second edition of his Treatise on the Principles of Human Knowledge. Berkeley divides 'ideas' - that is, direct objects of the mind - into three classes: perceptions, thoughts, and volitions. These types of ideas are distinguished by their source, as well as by their nature. Perceptions are those ideas that are imposed upon us from without (a crucial point in Berkeley's metaphysical argument; see my previous post): as long as my eyes are open, I perceive by sight, and I cannot (directly) control what ideas enter my mind in this way. Thoughts are ideas that are like perceptions except that they are produced by my own volition - I make them up. Volitions are the objects of the will which, among other things, produce thoughts. Like Locke, Berkeley believes that new simple ideas enter the mind only through perception, and our thoughts are created by putting simple ideas which we previously perceived together into different complex ideas.
Where Berkeley and Locke differ really substantially is in generalization. How is it that we are able to think about 'triangle' in general? Even more problematic for Berkeley is how we can think of spirits (Principles 27, 140) when these are not direct objects of the mind but, rather, are minds themselves and Berkeley has rejected the idea of any kind of resemblance between ideas and non-ideas (Principles 8ff.). Berkeley believes (and I am inclined to agree with him) that Locke's answer to the problem of generalization is virtually incomprehensible. Regarding "the general idea of a triangle," Locke says, "it must be neither oblique, nor rectangle, neither equilateral, equicrural, nor scalenon; but all and none of these at once" (Essay 4.7.9). On this section, Berkeley comments,
This is the idea which [Locke] thinks needful for the enlargement of knowledge, which is the subject of mathematical demonstraction, and without which we could never com to know any general proposition concerning triangles. That author acknowledges it doth 'require some pains and skill to form this general idea of a triangle.' ibid. But had he called to mind what he says in another place, to wit, 'That ideas of mixed modes wherein any inconsistent ideas are put together cannot so much as exist in the mind, i.e. be conceived.' [3.10.33] I say, had this occurred to his thoughts, it is not improbable he would have owned it to the above all the pains and skill he was master of to form the above-mentioned idea of a triangle, which is made up of manifest, staring contradictions. (Essay Toward a New Theory of Vision 125)
Nevertheless, there is the point of the phenomenology of the situation: we do, it seems, think about triangles in general, and not only particular triangles. How is this possible? Berkeley came to refer to his account of this phenomenon as 'general notions.' Things like spirits are not properly ideas, but we nevertheless mean something when we speak of them. As he says, "the words will, soul, spirit do not stand for different ideas, or in truth, for any idea at all but for something which ... cannot be like unto, or represented by, any idea whatever. Though it must be owned, at the same time, that we have some notion of soul, spirit, and the operations of the mind ... in as much as we know or understand the meanings of those words." (Principles, second edition, 27)
As he explains at New Theory of Vision 128 and elsewhere, Berkeley believes that these 'general notions' consist of two parts: a word or symbol, and a decision procedure. That is, when we talk about 'triangle' the symbol is the word 'triangle' either read or heard, or a picture of some particular triangle. Then we have some procedure by which, given any particular idea, we can determine whether it falls under this notion. When we reason 'abstractly' about triangles, we reason only from the 'essential characteristics' - that is, the characteristics specified in the decision procedure, namely, being a three-sided polygon. Ultimately, the symbols and decision procedures can be broken into simple ideas.
Of course, this doesn't exactly work for spirits, because there are no particular ideas that are spirits as there are particular ideas that are triangles, but the process is similar. We have certain 'relational notions' that are indeed general notions of how things might be related to one another and by applying these we can define spirits and so forth. In particular, a mind or spirit (Berkeley uses the two words more or less interchangeably) is that in which ideas inhere, and we have other examples of the inherence relation, and thus we can from an exceedingly vague general notion of a mind.
Now, why have I been thinking about this in connection with Kant? Well, Kant's conclusion in the Prolegomena (which I think I understand, even if I understand only pieces of the arguments for it) is that the proper objects of the understanding are "the possible objects of experience" and most metaphysics which has been done so far is based on attempts to go outside this boundary, which can lead to nothing but wild speculation. Instead, Kant believes, metaphysics must be 'reigned in' to it's proper domain: true metaphysics exists on the boundary of human reason, that is, at the point where the possible objects of experience come to meet the things which can never be direct objects of experience. By the nature of the boundary, we can conclude that at least some such things (e.g., the external world, souls, God) do in fact exist, and by examining the boundary closely we can come to conclusions about them. At sect. 57, Kant argues that "we can ... never cognize ... intelligible beings according to what they may be in themselves, i.e., determinately ... [but] we can still at least think this connection by means of such concepts as express the relation of those beings to the sensible world." He proceeds to take God as an example, and concludes that "we ... do not attribute to the supreme being any of the properties in themselves by whcih we think the objects of experience ... but we attribute those properties nonetheless to the relation of this being to the world." In sect. 58, Kant gives an example of such a relation and how it is understood by analogy: (1) as "the promotion of the happiness of the children ... "is to the love of the parents [so] ... the welfare of mankind ... is to the unknown in God ... which we call love." Thus Kant seems to me to say very much the same thing as Berkeley regarding the development of so-called 'abstract' ideas.
In conclusion: this is yet another example of how Berkeley doesn't get nearly enough credit, considering two very well known philosophers, Hume and Kant, seem to have received most of their best ideas, directly or indirectly, from him. Not to imply that Hume and Kant are unworthy of the credit they receive, but with regard to the ideas I find most impressive, Berkeley got there first. Kant's formulations are, on the whole, more precise and rigorous (one might even say that Kant brought new meaning to those words in the world of metaphysics), but they are also proportionately more opaque to those of us who have not yet had a chance to devote several years to studying them! Berkeley, on the other hand, is, for me, one of the easiest philosophers to read. So, enough of me - go read Berkeley!
 According to Kenneth Winkler's introduction to his abridged version of Locke's Essay, the Essay was required reading for BA students at Trinity beginning in 1692. Berkeley entered Trinity in 1700.
 See the editors' note on Principles 140 in Michael Ayers, ed., George Berkeley: Philosophical Works Including the Works on Vision.
 tr. Gary Hatfield
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