Empiricism

The traditional empiricists and rationalists were foundationists in epistemology. Foundationism postulates a base set of propositions that play a distinctive epistemic role plus a superstructure (comprising the bulk of our knowledge) appropriately related to the base. The empiricists and rationalists added the constraints that the basic statements must be certain and self-justifying (self-evident to reason for the rationalists and evident to the senses for the empiricists) and that the relation of base to superstructure be one of logical inference: deductive and perhaps inductive logic must suffice to generate the superstructure from the base. The justification is one-way or "linear" in the sense that the various layers of superstructure depend only on lower layers and, hence, ultimately on the base for their justification. Euclidean geometry provides the intellectual model. In this case the inferences are strictly deductive.

Given such a Euclidean geometry–inspired model, one wants the largest possible superstructure from the narrowest and most certain possible base. Two main problems stand in the way: the base problem (whether the base itself can be adequately justified) and the superstructure problem (whether the inferential resources are sufficient to support the desired superstructure on the base). From the beginning, empiricists have addressed the second problem by restricting the super-structure to claims within reach of observation and experiment and by developing the resources of logic, probability theory, and statistical inference. The British empiricists did not fully recognize the seriousness of the first problem.

Within this foundationist framework, Locke established the overall structure of a specifically empiricist theory in An Essay Concerning Human Understanding (1690), one of the founding works of the Enlightenment:

1. All simple ideas come from experience. There are no innate ideas. Contrary to nativists such as René Descartes (1596–1650), the mind is a tabula rasa—that is, a blank slate—at birth.
2. Ideas of solidity, movement, number, and so forth, resemble features of the real world (primary qualities), whereas sensations of color, sound, taste, and so forth, do not resemble the physical powers (secondary qualities) in objects that produce these sensations in the mind. They are mind-dependent.
3. Complex ideas are compounds of simple, atomic ideas, and, so, are image-like.
4. Thus knowledge, which is the intellectual recognition of the agreement or disagreement of ideas, cannot go beyond the limits of experience. (Locke's is an "idea empiricism," but knowledge requires an operation of mind in addition to the presence of ideas.)
5. Neither can meaningful language transcend experience, since the meaning of a word is an idea in the mind. Having the appropriate idea in mind is what distinguishes a person's from a parrot's uttering, "I want a cracker."
6. We each learn our native language by attaching public noises or marks (words) to ideas. We can then communicate our ideas to others by making the appropriate noises or marks.
7. Thought is a connected sequence of ideas.
8. The immediate objects of perception and thought are ideas in the mind, which in turn represent external things and situations (doctrine of representative perception, two-object theory of cognition).
9. All existing things are concrete and particular.

Empiricists immediately encountered the superstructure problem. Locke recognized that most meaningful words are general and many are abstract (rather than proper names of concrete objects, e.g., canine versus Lassie), so how do we get the corresponding ideas (meanings) from experience, which furnishes only particular ideas? From an image of a particular triangle, said Locke, we can abstract from its being equilateral, isosceles, or scalene, and thus construct a general idea of a triangle that is "all of these and none of these at once." Berkeley and Hume improved on this unsatisfactory solution, but to this day empiricist abstraction accounts face serious difficulties. Hume added to the superstructure problem by denying the adequacy of reason alone to produce, from particular experiences, either (a) moral judgments, about what one ought to do, or (b) inductive conclusions, such as "All ravens are black" and Newton's laws. The former is his point that one cannot deduce "ought" from "is" or value judgments from objective facts, and the latter is the aforementioned problem of induction. Meanwhile, Berkeley had challenged Locke's empirical base by rejecting his distinction between primary and secondary qualities.