My professor said that he believes the primary purpose behind Kant's Critique of Pure Reason is to respond to the empiricist view that morals are ultimately subjective.

He believes that the primary purpose behind Kant's epistemology is to show that through transcendental idealism and through the possibility of synthetic a priori knowledge, there is a certain truth that lies within all humans and that there thus must exist "a moral truth."

Is this likely true? And if so, what evidence is there in Kant's CPR to show that his philosophy is indeed primarily about morals?

  • 2
    What you describe better fits Critique of Practical Reason. Critique of Pure Reason mostly uses the possibility of synthetic a priori knowledge to show that there is certain knowledge about nature and mathematics, not ethics. As for the underlying motivation, Kant explicitly writes "I have therefore found it necessary to deny knowledge, in order to make room for faith". He circumscribes synthetic a priori knowledge so as to leave religion out of it.
    – Conifold
    Commented Dec 20, 2018 at 20:26
  • It might be argued that his primary purpose was to refute scepticism, this being his hated 'scandal of philosophy'. As an ethical theory would require a metaphysical foundation I see no point in distinguishing between ethics and metaphysics.
    – user20253
    Commented Dec 21, 2018 at 13:50

2 Answers 2


As a statement of 'the primary purpose' of Kant' philosophy, if it had one (just one), this seems implausible.

Something closer to the truth would be that Kant sought to combine rationalism and empiricism but even this is not quite right. Both rationalism and empiricism had irremediable flaws in Kant's view. None the less each contained elements of truth which could be transformed and incorporated into what Kant eventually presented as his Critical philosophy. ('Critical', briefly, because it was set out in Critiques.)

Kant's main grouse was that rationalism sought and claimed knowledge of a non-empirical reality - God, for one thing in Descartes' case. Empiricism in contrast sought to derive all knowledge ultimately from experience. For various reasons Kant believed this to be a false account; only if filtered or structured by 'categories of the understanding', not themselves in any way derived from experience, could sense impressions cohere into anything that amounts to experience. The experience of space and time also requires 'forms of intuition' by which the understanding can experience anything spatially or temporally.

It's a long story but Kant's fundamental concern is to show how the Critical philosophy alone can explain how everyday and scientific knowledge is possible. This concern had nothing directly to do with ethics. Or at least its central motivation was not ethical; Kant was here working principally as an epistemologist.

Kant did intend in his major epistemological (and metaphysical) work, The Critique of Pure Reason (1781/ 1787), to include an examination of the principles of ethics. This was actually accomplished mainly - only mainly, because other, later works were also relevant - in the Groundwork of the Principles of Morals (1785) and The Critique of Practical Reason (1788). Ethics was of vital interest to Kant, and certainly no mere add-on to the other work. Opposed to ethical subjectivism, he argued that ordinary moral judgement - Kant takes morality as he (thinks he) finds it - can be objective but only if it contains an a priori element - an element not derived from experience. This element is one of rationality which branches out into the categorical imperative and its various formulations. When Kant insists that we must act in such a way that it is logically possible for everybody else to act in the same way, this idea is not something we can acquire from experience. How could be perceive this ? Yet nor is it rational' in the manner, say, of a Cartesian clear and distinct idea detached from action. But it is rational - practically rational - because it involves consistency, the consistency of everybody's being able to act in the same way.

Kant had a nexus of concerns. These interlocked within and between texts and ethics was always of profound importance. But I think it is an impoverishment of the Critique of Pure Reason to read it purely or even mainly as a prolegomenon to ethics.

  • i upvoted, not cos i know you're right, but cos it sits with me: it seems wrong to say that kant's influence etc. was basically just in morality
    – user35983
    Commented Dec 22, 2018 at 6:54

Compare : I.Kant, Prolegomena to Any Future Metaphysics (1783), Preface :

My intention is [...] to pose the question: “whether such a thing as metaphysics is even possible at all.”

If metaphysics is a science, why is it that it cannot, as other sciences, attain universal and lasting acclaim?

with I.Kant, Groundwork of the Metaphysic of Morals (1785), Preface :

Ancient Greek philosophy was divided into three sciences : PHYSICS, ETHICS and LOGIC.

All rational cognition is either material and considers some object, or formal and occupied merely with the form of the understanding and of reason itself, and with the universal rules of thinking as such, regardless of differences among its objects. Formal philosophy is called LOGIC [...].

All philosophy in so far as it is based on grounds of experience can be called empirical, that which presents its doctrines solely from a priori principles pure philosophy. The latter, if it is merely formal, is called logic; but if it is limited to determinate objects of the understanding it is called metaphysics.

In this way there arises the idea of a twofold metaphysics, a metaphysics of nature and a metaphysics of morals. Physics will thus have its empirical, but also a rational part; so too will ethics, though here the empirical part might in particular be called practical anthropology, the rational part actually moral science.

This is a sketch of Kant's "foundational project".

In 1786 he published the Metaphysical Foundations of Natural Science, followed in 1797 by The Metaphysics of Morals.

We have to recall also Kant's lectures Anthropology from a Pragmatic Point of View, published in 1798.

Of course, Kant's philosophy evolved over time, but all is mature works must be collacated into an overall project encompassing all philosophical and empirical sciences.

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