(a) What are the basic tenets of Rationalism ? How does Descartes build a system of Philosophy in consonance with them ? Discuss…

(a) Rationalism and Descartes’ philosophical system

Rationalism posits that unassisted reason, rather than sensory experience, is the primary source of substantive knowledge. Its core tenets are the existence of innate ideas, the reality of necessary truths discoverable independently of experience, and the adoption of the geometrical-deductive method to construct a secure system of philosophy.

René Descartes rigorously implements this rationalist framework. Through his method of universal doubt (methodic doubt), he dismantles all empirical and dubitable beliefs to discover an indubitable foundation: Cogito, ergo sum (I think, therefore I am). From the self-authenticating certainty of the thinking subject, Descartes extracts the epistemic criterion of truth: whatever is perceived with clarity and distinctness is necessarily true.

To bridge subjective certainty with the objective existence of the external world, Descartes offers two proofs for the existence of an infinitely perfect God: the causal "trademark" argument of Meditation III (the idea of an infinite being can only have been caused by such a being) and the ontological argument of Meditation V (existence belongs to the essence of a supremely perfect being). Because God is benevolent and not a deceiver (veracitas Dei), human cognitive faculties—when operating under clear and distinct perceptions—are epistemically reliable. God serves as the ultimate guarantor of necessary truths and the objective existence of extended matter (res extensa), thus completing Descartes' dualistic rationalist system, built like geometry from first principles (Descartes' own image is the tree of philosophy, with metaphysics as the roots, physics as the trunk, and medicine, mechanics and morals as the branches). Arnauld's objection of the "Cartesian circle" (clear and distinct perception proves God, and God guarantees clear and distinct perception) remains the main difficulty for the system.

(b) Spinoza: "All determination is negation"

In Spinoza’s pantheistic substance monism (Deus sive Natura), only one infinite, unconditioned substance exists. Attributes constitute the essence of this substance, while individual finite things are modes—determinate modifications of substance under the attributes of Thought and Extension.

Spinoza's dictum determinatio negatio est (Letter 50 to Jarig Jelles, 1674, where he says that figure is a determination and determination is negation) signifies that every finite determination is fundamentally a limitation. To determine a finite mode as having a specific form A necessarily negates and excludes its being non-A. A finite entity is defined not by self-subsistent being, but by what it lacks relative to the infinite totality.

This is why substance itself cannot be determined: it is "absolutely infinite" (Ethics I, Definition 6), and to limit it would be to negate it. A thing is "finite in its own kind" when it can be limited by another thing of the same nature (Ethics I, Definition 2): a body is limited by another body, a thought by another thought. Hegel generalised the dictum as omnis determinatio est negatio and read Spinoza as an acosmist, for whom finite things vanish into the undifferentiated Absolute. Defenders reply that Spinoza affirms the reality of modes, which follow necessarily from God's nature (Ethics I, P16) and have a positive striving (conatus, III P6); negation marks only the limitation of a finite mode, not its unreality.

(c) Hume’s critique of causation and Kant’s response

David Hume dismantled rationalist causation by demonstrating that causal relations are neither intuitive relations of ideas nor directly perceived matters of fact. Experience provides only impressions of spatial contiguity, temporal priority, and constant conjunction between events; it never reveals an objective "necessary connection." Hume concluded that causal necessity is merely a psychological fiction—an instinctive habit of mind and customary association generated by repeated experience, thus driving epistemology into skepticism.

Immanuel Kant’s "Copernican Revolution" salvaged objective knowledge by reconciling rationalism and empiricism. Kant acknowledged that while all knowledge begins with experience, it does not arise from experience. He identified causality as a pure a priori category of the understanding. Causality is a synthetic a priori rule that the mind actively imposes upon sensory intuition (manifold) to synthesize it into coherent, lawful experience. In the Second Analogy of Experience he argues that we can distinguish an objective succession of events (a ship moving downstream) from a merely subjective succession of perceptions (scanning a house) only if the order is fixed by a rule, the causal rule. Kant thus resolved Hume's challenge by distinguishing between metaphysical causation (which illegitimately seeks to know things-in-themselves or noumena) and scientific causation (which transcendentally grounds the universal, necessary laws governing the phenomenal world). The price is transcendental idealism: causal necessity holds for phenomena only, and whether things in themselves are causally connected cannot be known.