A. Descartes: idealist in method, realist in intention. Tried to build a bridge from thought to reality. Implicitly made knowing (thinking) the condition of being.
B. Malebranche. Discovered that transitive causality (from one substance to another) within the created order made no sense, from an idealist perspective. Adopted occasionalism: God causes everything, secondary "causes" are only occasions for Divine activity. (MR, 89)
B. Berkeley. Denies the existence of matter. Everything physical is a system of ideas in God's mind. Finite spirits do exist, and do exercise real causation (in the exercise of their will).
C. Hume extended Malebranche's occasionalism to God, undermining any causal argument for God's existence. Causation is nothing more than the regular succession of ideas in space & time. No room for "metaphysical" causes -- not even within the mind. The "will" consists merely in the perceived sequence of mental states. (MR, 90)
D. Kant's Copernican Revolution: the world of nature must conform to the requirements of human knowledge. We can't know "things-in-themselves", only the appearances things have for us. Causation is prescribed for the world of nature by the human mind. Kant rejects Berkeley's "subjective idealism": even time, and the introspectible mind, are merely appearances to a "transcendental" self.
E. Hegel's absolute idealism. Criticizes Kant's naive realism, embodied in his belief in things-in-themselves that somehow cause sensations in us. By Kant's own standards, such "noumena" are unthinkable. The so-called "appearances" are the only reality. Reality consists in the evolution of the human spirit (social, not merely individual), overcoming a series of contradictions or antinomies, and culminating ultimately in Hegel's own philosophical System.
F. The logical positivists turned back to Hume. All that we can know are sense "data" (sensations) and things "logically constructed" out of sense data. All meaningful propositions can be translated into predictions about future sequences of sensations. All "metaphysical" propositions are meaningless (including Kant's talk of noumena, or Hegel's of an absolute spirit).
A. Idealism contradicts common sense. There is no such thing as naive idealism -- there is not even such a thing as natural idealism. (119, 135)
B. Idealists can't be consistent to their own principles. They persist in making metaphysical judgments. (114-115)
C. Idealism leads reason into a series of insoluble antinomies (contradictions). (35, 85-88, 92-96)
D. Idealism uncritically and dogmatically adopts a particular method in advance of any encounter with the facts. Realism adopts its methods (plural) from the facts. (99, 116-7)
E. Idealism results from a failure to respect the objects of knowledge: "Respecting the object of knowledge means, above all, a refusal to reduce it to something which complies with the rules of a type of knowledge arbitrarily chosen by ourselves." (142)
F. Idealism results from an impatience, a misdirection of the passion to know (a moral flaw) The idealist "wants to reduce reality to knowledge so as to be sure that its knowledge lets none of reality escape." (140) Contrast: the humility/modesty of the realist, who knows his knowledge to be neither infallible nor exhaustive.
G. The Proofs of Idealism are sophistical. The problems idealism purports to solve are all products of idealism itself.
A. The senses give knowledge of particular, material things. There is no separate, inner object that merely represents or copies the external thing. When the senses are working properly, they give direct knowledge of the thing itself.
B. All concepts are in some sense "abstracted" from this sensory knowledge. Crucially, this process of abstraction produces the concept of causation (contrary to Hume). Concepts are not simply pale copies of sensations, as Hume thought.
C. Each aspect of reality calls for its own proper method of inquiry. There is no such thing as the scientific or the philosophical method. Our methods are refined through greater familiarity with the nature of things. The critical error of scholasticism was to follow Aristotle in making biological method universal, nullifying the sciences of physics and chemistry. (98)
D. Epistemology (the theory of knowledge) is not prior to other sciences or the rest of philosophy. Epistemology and ontology should grow together. The different parts of true philosophy mutually reinforce one another. (Neurath's raft) (35)
E. The transcendentals (the good, the true, the beautiful) are not "values" to be grounded somehow in fact. Rather, they are themselves aspects of being: being as desired, being as known, being as admired. (123, 141) "For the realist, the only principle which can determine the way things ought to be is the essence which causes them to be what they are."