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

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 (de omnibus dubitandum), 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 formulates the ontological and cosmological proofs for the existence of an infinitely perfect God. 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.

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 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 principle provoked substantial philosophical debate. G.W.F. Hegel interpreted Spinoza’s dictum as reducing the finite world to sheer illusion or unreality that is dialectically absorbed into the undifferentiated Absolute. In modern scholarship, Harold Joachim aligns with this view, seeing determination as privation and metaphysical limitation. Conversely, Harry Wolfson argues that for Spinoza, determination does not denote sheer non-being, but the positive, actualized essence of a mode within the deterministic causal order of Nature, treating negation as a logical delimitation rather than ontological unreality.

Hume’s Critique of Causation and Kant’s Transcendental 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. 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 movement from Descartes' foundational rationalism through Hume's empirical skepticism to Kant's critical philosophy demonstrates the trajectory of modern epistemology: shifting from metaphysical speculation about substance to a transcendental inquiry into the conditions and limits of human cognition.