This paper is the winner of the first annual Colin and Alisa Turbayne International Berkeley Essay Prize Competition.
1. Berkeley's official dualism of spirits and sensibles and the implicit monism it conceals are discussed in my "Berkeley's Unstable Ontology." The Modern Schoolman 67 (1989): 15-32. The role of the Manifest Qualities Thesis in his metaphysics is there touched upon, but not examined in detail.
2. Berkeley contrasts perceiving a spirit with having one marked out by what we do perceive and rejects the possibility of doing the former. "Mark out" seems to mean provide an observational ground for an inference to what cannot itself be perceived. The text quoted is The Works of George Berkeley, ed. A. A. Luce and T. E. Jessop (London: Thomas Nelson and Sons Ltd., 1964), vol. 2. It will hereafter be cited as Works.
3. In an editorial note, no. 1, at Works, 2: 51, T. E. Jessop says the words "since they and every part of them exist only in the mind, it follows that there is nothing in them but what is perceived" express a modern axiom. To me they seem to be a controversial enthymeme, whose implied major premiss is that whatever exists only in the mind is only what it is perceived to be.
4. To my knowledge no one has examined in depth the status of animals in Berkeley's philosophy and the specific issue of whether for him one can infer animal perceivers or thinkers from the sensible bodily states of animals, as one presumably can infer human perceivers from their sensible bodily states. Perhaps we need to take seriously the possibility that Berkeley was defending his own special version of the Cartesian "beast machine" hypothesis.
5. In Section 2 of his Essay towards a New Theory of Vision (hereafter NTV), Berkeley asserts as well-established and commonly held the thesis that distance is never immediately seen. (See Works, 1: 171). Subsequently he maintains without explicit argument that what is immediately seen is at no distance whatsoever from its perceiver. (See NTV, sects. 41 and 45; Works, 1: 186-88, for example.) The question, why cannot a visual, an immediate object of sight, be at some distance from its perceiver even though its distance is not immediately seen, can be generalized as the following questions: First, can an object of immediate perception have a quality which is perceivable, but which it is not immediately perceived to have? Second, can an object of immediate perception have an imperceptible quality? For a discussion of these questions as they pertain to distance, see my "On the Status of Visuals in Berkeley's New Theory of Vision," in Essays on the Philosophy of George Berkeley, ed. Ernest Sosa, Synthese Historical Library/Volume 29, (Boston: D. Reidel Publishing, 1987), 165-94.
6. An indirect realist might hold that material things are perceived insofar as they are represented in consciousness by effects which they produce. On this view sensibles (understood as those effects) might be held to exist only in or as elements of consciousness. Idealism, as I am using the term, characterizes sensible objects as elements of consciousness, even though it might challenge the supposed causal linkage between sensibles and material objects. For the idealist, a sensible cannot exist when unperceived or outside consciousness. Two other comments: First, idealism is not to be equated with immaterialism, the denial of material substances. Second, Berkeley must hold that an idealistic account of sensibles does not presuppose indirect realism. Were it to do so, his basic principle for rejecting the existence of material substances would presuppose the existence of such substances.
7. Berkeley sometimes uses "idea" simply to mean sensible object (sensible). That sense cannot be of relevance to the present discussion. If by idea one simply means sensible, one can hardly argue that no sensible is a perceiver because it is merely an idea. A similar problem holds for the argument that sensibles cannot be active. Berkeley also says he calls sensibles ideas because they are inactive and senseless; obviously, this sense presupposes the soundness of the arguments...