In the following, I focus on Locke's arguments against the rationalist position of innate epistemic principles in An Essay Concerning Human Understanding (1689). For a concise overview of Locke's Essay, see Carl Stahmer's piece in The Pre-History of Cognitive Science (external). A broader discussion that situates the debate between rationalism and empiricism in the context of cognitive culture theory can be found under Empiricism vs. Rationalism: The Debate Continues.
The scope of Locke’s investigation
Locke at the outset adopts a computational approach, rejecting the materialist (he will not "meddle with the physical consideration of the mind") and the theological (he will not speculate "wherein its essence consists"): his concern is with "the original [origin], certainty, and extent of human knowledge, together with the grounds and degrees of belief, opinion, and assent" (1). By "knowledge" he means the ability to know, the faculty of gathering and utilizing information; to understand its "extent" is significant because it can lead men to realize what they cannot know, and thus "to sit down in a quiet ignorance of those things which, upon examination, are found to be beyond the reach of our capacities" (2). More generally, we should "entertain all objects in that way and proportion that they are suited to our faculties" (3). Holding out the hope that we will learn the proper use of our limited capacities and specifically human faculties by seeing "to what things they were adapted" (4), Locke is looking for what we might call the computational specifications, the design of the human mind.
The arguments against innate ideas
Situating himself against the rationalists, Locke begins by challenging the "established opinion among some men, that there are in the understanding certain innate principles" (12). In the following, I focus exclusively on the arguments against epistemic rationalism, leaving aside the highly interesting claims of ethical rationalism for the moment. Based on a model of the understanding as a set of propositions present to consciousness consisting in impressions on an unstructured substrate, he demonstrates convincingly there are no innate ideas present from birth.
The assumption of cognitive transparency
Cognition, in Locke's view, consists in ideas, by which is meant "nothing but the immediate objects of our minds in thinking" (6)--the common-sense assumption that consciousness is the mind, that all cognition takes place at the site of phenomenological awareness. True, Locke himself remarks in the opening paragraph, "The understanding, like the eye, whilst it makes us see and perceive all other things, takes no notice of itself; and it requires art and pains to set it at a distance, and make it its own object" (1); however, the assumption that what is needed is careful introspection remains.
The metaphor of the wax tablet
Once cognitive transparency is assumed, the conscious content of the mind becomes the test of innate ideas, "for to imprint anything on the mind, without the mind's perceiving it, seems to me hardly intelligible" (13). In this metaphor, the assumption that the clay itself has no structure is already implied; the search for prior structure limits itself naturally to conscious impressions.
The understanding as a set of propositions
In a related move, the understanding is tacitly equated with the conscious product of understanding—knowledge, conceived as a set of propositions. This makes the claim of cognitive transparency seem more plausible; it is only common sense to hold that "No proposition can be said to be in the mind which it never yet knew, which it was never yet conscious of." (13). If you can die without realizing you know something, "this great point will amount to nothing more, but only to a very improper way of speaking" which in practice "says nothing different from those who deny innate principles" (14).
Innate ideas as fully present at birth
The innate ideas Locke argues against are those which "the soul receives in its very first being, and brings into the world with it" (12). A simple test of the rationalist hypothesis is thus to inquire into the ideas of "children and idiots"; if it is granted that they have souls, it follows that these should be impressed with innate ideas. Since it is simple to ascertain that children do not have certain ideas-- such that the proposition that "it is impossible for the same thing to be, and not to be" (13)--by asking them, or by appealing to common knowledge of children, the presence of innate ideas can swiftly be ruled out.
Locke’s critique of rationalism flows coherently from his underlying assumptions of the understanding as
It is Locke’s assumptions rather than his explicit reasoning that is problematic. These form a cluster; the notion that the understanding is a product rather than a process follows from the common-sense assumption of cognitive transparency, since it is precisely the products of cognition, rather than its inferential processes, that are made available to consciousness. Locke’s achievement lies in the computational approach itself: what he establishes is the possiblility of thinking about the mind as an information processor. Since the operation of the mind’s faculties are typically unavailable to introspection, the assumption of cognitive transparency makes the rationalist position, particularly in Locke’s formulation, untenable at the outset.
What Locke is unable to get at within the framework of these assumptions is a conception of a specified faculty. It strikes him as self-evident that humans have a general capacity to acquire propositions, but this fact should be clearly distinguished from the claim of innate ideas (14).
The commonsense assumption of cognitive transparancy is not challenged
until Hume, whose introspective experiments begin to push past the limits
of conscious awareness. This simultaneously undermines the notion that
the understanding is a product, consisting in propositions; rather, it
is a process, where the power of making inferences (Hume’s celebrated Problem
of Induction) requires an explanation. It is the search for this explanation
that leads Kant to a formulation of transcendental categories.
1. By "adapted", Locke means "suited" in a general sense; the coincidence with the terminology of evolution is of course accidental, and the notion of design, if he felt it needed an explanation, would receive one from theology. [Back]