(a) Is rejection of Locke's notion of primary qualities instrumental in Berkeley's leaning towards idealism ? In this context…

(a) Berkeley, Locke and Hegel

Locke distinguishes primary qualities—extension, solidity, motion—from secondary qualities such as colour and taste. Primary qualities are mind-independent; secondary qualities are mind-dependent sensations. Berkeley’s rejection of this distinction is instrumental in his immaterialism because he argues that even primary qualities cannot be conceived apart from perception. First, the relativity argument that Locke used for secondary qualities applies equally to primary ones: size, shape and motion vary with the perceiver's position and state. Second, extension cannot be conceived without some colour or tactile quality, so primary and secondary qualities stand or fall together. Third, the 'abstract idea' of matter stripped of all sensible qualities is unintelligible. His master argument holds that one cannot think of an object as unperceived, since thinking of it is already perceiving it. If extension and solidity are inseparable from perceived ideas, there is no material substratum. Hence esse est percipi: finite objects exist only in being perceived, and their continued existence is secured by God. Thus perception becomes the ontological condition of existence.

Berkeley’s subjective idealism differs from Hegel’s absolute idealism. Berkeley’s world depends on finite perceivers and ultimately on God; reality is grounded in a personal divine mind. Hegel does not reduce reality to finite subjects. His absolute idealism understands reality as the dialectical unfolding of Geist through history, logic, nature and spirit. For Hegel, the absolute is not a perceiver of ideas but the rational whole coming to self-consciousness; subject and object are moments in its development, not opposed as mind and matter.

(b) Spinoza: "Whatever is, is in God"

Spinoza establishes that God alone is absolutely real by defining substance as causa sui and God as absolutely infinite, not merely infinite in its kind. Substance is what is in itself and conceived through itself; a mode is what is in and conceived through another. Two substances cannot share an attribute (E1P5); substance is necessarily infinite and exists by its own nature; God, having all attributes, necessarily exists (E1P11). Hence 'except God no substance can be or be conceived' (E1P14), and 'whatever is, is in God' (E1P15). Thought and extension are attributes of one infinite substance, not separate substances, thereby rejecting Cartesian dualism. “Whatever is, is in God” means that all finite things are modes, i.e. modifications of God’s attributes, not independent beings. Natura naturans is God as the active causal ground; natura naturata is the system of modes following from God’s nature, not God as an effect. This yields the formula Deus sive Natura: God is the immanent, not transitive, cause of all things, not a transcendent personal creator.

Critically, the demonstration is rigorous given its definitions, but those definitions carry the conclusion. It is unclear how finite, particular modes follow from an infinite substance. Hegel charged Spinoza with 'acosmism' (the world is swallowed in God), while contemporaries saw atheism in it; others read it as pantheism or panentheism. Human freedom reduces to understanding necessity, and individuality and evil lose independent standing.

(c) Kant's objections to the ontological argument

The argument (Anselm, Descartes) holds that the concept of a supremely perfect or necessary being includes existence, so God must exist. Kant replies, first, that if 'God exists' is analytic, then rejecting the subject together with its predicate involves no contradiction; necessity attaches to judgments, not to things. Second, all existential propositions are synthetic, so no concept alone can guarantee existence. A real predicate adds something to the concept of a subject; existence, however, is not a real predicate. To say “God exists” does not add a further property to the concept of God; it posits the object as actually given. His thalers example shows that one hundred real thalers contain no more predicates than one hundred possible thalers. He also distinguishes the “is” of predication from the “is” of existence, arguing that the argument confuses logical with real possibility: consistency does not imply reality.

Yet Kant’s critique must be examined critically. His thalers example concerns contingent objects, whose existence is merely posited; it may not apply to a necessary being, whose essence includes existence. If necessary existence differs from contingent existence, the argument may target a different kind of being. Hegelian responses reject the separation of concept and existence by treating existence as a moment of the absolute idea; Plantinga-style modal arguments reformulate it: if maximal greatness includes necessary existence in some possible world, then God exists in all worlds. Kant’s objection is powerful against the traditional move from concept to fact, but it does not refute every ontological reconstruction.