Perceptual knowledge

This chapter critically analyzes Locke’s views on “sensitive knowledge.” Its main theses are: (1) Locke sometimes confuses the legitimate question (Q1), “When we perceive a body, how can we know that we aren’t hallucinating instead?” with the faulty “veil-of-perception” question, (Q2) “How do we know bodies exist, since we can’t perceive them?” (2) When Locke does mention (Q1), he sometimes just dismisses it, because he holds that simple ideas of sensation are by definition produced by bodies. (3) At other times, Locke humors the skeptic, and offers a defense of the senses, in the form of an inference to the best explanation. (4) It’s doubtful that he could successfully rule out other possible explanations of our perceptual experience, like Descartes’s deceiver scenario and its contemporary variants. (5) There are reasons for this weakness, and they carry over to any attempt to defeat skepticism by an inference to the best explanation.

The problem of perception

This chapter formulates the problem of perception, which Locke sometimes dismisses but eventually tries to solve. The formulation hinges on the “argument from the multiple possible causes of any perceptual experience,” which shows that no physical thing can be “immediately perceived,” i.e., known to exist solely on the basis of one’s current perceptual experience. This conclusion generates a regress, since any experience one might appeal to for corroboration also has multiple possible causes. The problem can’t be avoided simply by adopting a two-term rather than a three-term theory of perception, because perceptual experiences can be phenomenologically indistinguishable whether they are caused by a physical object affecting one’s sense-receptors or caused otherwise. This has led to the traditional question: can knowledge of physical things be legitimately inferred from knowledge of immediately perceived ideas, sensations, or “sense-data” (on a three-term theory), or of ways of being “appeared to” (on a two-term theory)?

Language

This chapter addresses Locke’s views about language and meaning. His fundamental thesis is that “names” (referential and descriptive or “general” words) signify ideas, which represent things and properties. The ideas that general words signify are abstract ones, formed by abstracting common characteristics from perceptual encounters with particular things and from introspected experiences. Abstract ideas of substances are identical with their nominal essences, which are ideas of the observable qualities by which we classify substances as falling into sorts, and which Locke distinguishes from substances’ real essences, which are unknown microscopic properties (probably of corpuscles) in virtue of which things have those observable qualities. The chapter discusses the privacy of ideas, George Berkeley’s objection to abstract ideas, the significance of the distinction between nominal and real essences, Locke’s rejection of substantial forms, and Locke’s reasons for holding that names of substances signify their nominal rather than their real essences, contrasting this position with Saul Kripke’s now-influential opposing view.

Identity

This chapter expounds, formulates in analytical style, and defends Locke’s general view of identity. It interprets Locke’s puzzling statement that existing at the same time and place isn’t necessary for synchronic identity. It focuses mainly, following Locke, on diachronic identity. Locke never suggests that X is diachronically identical with Y iff they house the same substance-substratum; indeed his account of diachronic identity undermines the argument from change for substance-substratum. For Locke, X is diachronically identical with Y iff X is spatiotemporally continuous with Y, and every segment of the space-time path between X and Y is occupied either by something of the same sort as X or by something of the same sort as Y. This account applies to inanimate objects, plants, and animals. Its appeal to sortals makes it a version of the “relative identity” view. The chapter defends that view against the charge that it is self-contradictory.

The Origin and Classification of Ideas

This chapter (1) expounds Locke’s empiricist principle that all of our ideas are derived from experience, and (2) offers a clarification of the structure of Book II of the Essay. Regarding (1), it explains his twofold use of the term “idea” to mean both any sensory or introspectible state and any concept, his distinctions between ideas of sensation and ideas of reflection and between simple and complex ideas, and his classification of simple ideas. It identifies some noteworthy points about the idea of solidity. Regarding (2), it provides a clarification of the organization of Book II, in light of the facts that Locke (a) digresses into the theory of primary qualities and secondary qualities in Book II Chapter viii before continuing his aetiology of ideas, and (b) discusses several complex ideas of reflection, in Book II Chapters x and xi, before officially turning to complex ideas in Chapter xii.

Locke’s epistemological turn and his polemic against innatism

This chapter explains Locke’s stance that we should examine our own powers of knowing before tackling the big metaphysical and moral questions, and analyzes his attack on the doctrine that basic logical, metaphysical, and moral principles are innately known. It argues that this attack is not directed against a straw man, and describes the motivation for it. It explains the difference between the “naïve” or occurrent version and the dispositional version of innatism and the difference between speculative principles and practical principles. It analyzes Locke’s critique of what he regards as the chief argument for innatism, the argument from universal consent. It expounds his critique of both occurrent innatism and dispositional innatism, and of both types of allegedly innate principles. It suggests that the attack on dispositional innatism needs to be supplemented by Locke’s positive view about the acquisition of our ideas in order to be compelling.

Knowledge in general

This chapter explains: (1) Locke’s definition of knowledge as idea-agreement; (2) his four species of knowledge— identity/diversity, relation, co-existence/necessary connection, real existence; (3) his three degrees of knowledge—intuitive, demonstrative, sensitive; (4) his view of the extent of knowledge for each species; and (5) his view about the reality of knowledge. It notes that the first three species of knowledge cover mostly generalizations, whereas the last species covers existence claims. It discusses the extent of knowledge in each of the first three species. It explains why Locke thinks that knowledge of co-existence (which is knowledge of substances’ properties) is “very small,” leaving sensitive knowledge for the last two chapters. It argues that although Locke’s discussion of the reality of knowledge accommodates mathematical and possibly moral generalizations well enough, it does not fit laws of science, and misleadingly invites us to think of them as a priori truths rather than empirical truths.

Personal identity

This chapter analyzes Locke’s seminal treatment of personal identity and examines objections to it and replies to them. It (1) discusses his sharp divorce between a person’s identity and the identity of any substance, (2) formulates in analytical style his definition of personal identity in terms of memory, and (3) explains his view that personal identity is a “forensic” notion. Regarding (1), it argues that although Locke’s same substance/different person scenario makes sense, his same person/different substance scenario crosses the bounds of sense. Regarding (2), it shows how a definition of personal identity in terms of memory can be refined so as to avoid counterexamples proposed by Berkeley, Thomas Reid, and John Perry. Regarding (3), it argues that such a refined definition is incompatible with Locke’s forensic view of personhood, unless one appeals to Christian doctrine about the afterlife and about Judgement Day—as indeed Locke was prepared to do.

Complex Ideas

This chapter discusses complex ideas, concentrating on those Locke calls modes, arguing for a non-idealist interpretation of those he calls relations, and introducing the one he calls substance. It analyzes the simple modes—space, time, and number—by untangling Locke’s language, which leaves unclear whether they are modes of the simple idea from which they are constructed (e.g., making 117 mode of 1) or of a general idea under which they fall (e.g., making 117 a mode of “number”), and by addressing questions about the simplicity of the ideas from which they are constructed and about the simple modes’ infinity. It contrasts them with mixed modes and discusses the latter’s construction. The chapter defends James Gibson’s view that for ideas of reflection, the relation between mode and simple idea isn’t that of whole to part, but of a universal to its determinations (e.g., making “remembrance” a mode of “perception, or thinking”).

Primary and Secondary Qualities

This chapter expounds Locke’s theory of primary qualities and secondary qualities and defends a modernized version of it. It argues for the following theses. Although Locke defines secondary qualities as powers in objects to produce in us ideas of color, sound, taste, smell, heat, and cold, he oscillates between equating colors, sounds, etc. with (a) those powers and with (b) the ideas they produce in us. This oscillation stems from Locke’s wanting to say that they are both (a) and (b), despite his basic cleavage between ideas and qualities. Such a hybrid view of them is plausible, especially if we drop the three-term theory of perception often attributed to Locke in favor of a two-term theory, which says that the last term in the perceptual causal chain is the object’s appearing some way to the perceiver, and which distinguishes this “manifest aspect” of a secondary quality from its “dispositional aspect.”