René Descartes and John Locke, both seventeenth century philosophers, are often seen as two of the first early modern philosophers. Both Descartes and Locke attempt to find answers to the same questions in metaphysics and epistemology; among these: What is knowledge? Is there certainty in knowledge? What roles do the mind and body play in the acquisition of knowledge?
Descartes and Locke do not provide the same answers to these questions. In this paper I will consider the similarities and differences between the philosophies of Descartes and Locke. I will first briefly consider several similarities. I will then discuss a few important differences in their theories of knowledge (namely the distinction between rationalism and empiricism and the question of the existence of innate ideas). Finally, I will consider the more subtle distinction between the Cartesian and Lockean accounts of self, the role of the mind, and the mind/body distinction. Having enumerated similarities and differences, I will conclude that Descartes and Locke offer fundamentally different philosophies.
Part I:
Although I maintain that the philosophies of Descartes and Locke are different, this does not exclude the possibility of similarities. In fact, I believe there are many points of agreement between Locke and Descartes. Locke's Essay Concerning Human Understanding is not a direct attack on Descartes; in contrast, it is an account of epistemology which, though not Cartesian, was influenced in part by Locke's reading of Descartes. Locke borrowed many of Descartes' philosophical ideas and objections and adopted much of his terminology.
I will now consider four passages in which Locke appears to be drawing on Descartes: the notions of ideas and qualities, the importance of language and reason, God and the will, and universals and classification. (Note that in these cases differences as well as similarities may be found, but I am here choosing only to address the similarities.)
Locke's notion of the idea is one example of a term borrowed from Descartes. For Locke, an idea is that which ``the mind perceives in itself, or is the immediate object of perception, thought, or understanding'' (Locke, 48). This seems to be exactly Descartes' definition of idea: ``whatever is immediately perceived by the mind'' (Descartes, 132). Locke then goes on to consider the qualities (powers to produce ideas) of external objects. He distinguishes between primary and secondary qualities; the latter are those which are not in the objects themselves but are perceived or sensed, while the former are those which cannot be separated from the object and belong to it at all times such as solidity, extension, figure, and mobility (Locke, 49). This echoes the distinction made by Descartes about the qualities of wax. Descartes clearly perceives (the having of) size, shape, and number, as well as motion, substance, and duration, but qualities such as color and sound (Locke's secondary qualities) are not as clearly perceived (Descartes, 92).
For both Descartes and Locke there is something about man which sets him apart from machines and animals. Descartes says that though machines may superficially appear to imitate man, they could still be discerned from real men with certainty. Machines, he says, ``could never use words, or put together other signs, as we do in order to declare our thoughts to others'' (Descartes, 44). Nor can animals (beasts), as they have not only less reason than men, but no reason at all (Descartes, 45). Compare this with Locke's claim that animals (brutes) ``have not the faculty of abstracting, or making general ideas, since they have no use of words'' (Locke, 64). In both Descartes and Locke, I see precursors for theories of the importance of reason and language.
Descartes and Locke both discuss free will; in particular, they consider how it is that our will may be both directed and remain free, and how it is consistent with the existence of a God that we can err in our ways. On the first of these points, Descartes thinks this does not limit our freedom; instead he believes that the more one inclines in one direction, the more free the choice is. On the second point Descartes believes that the imperfection is not one from God, but that our intellect is not as great as our will (Descartes, 101). Locke picks up on these sentiments, agreeing that for us as well as God ``to be determined by [one's] own judgment is no restraint to liberty'' (Locke, 106). Locke extends Descartes yet again by explaining that bad choices may arise from bad judgments (Locke, 110).
