Kant’s Practical Extension of Reason

Part V: The Practical Extension of Reason and Traditional Metaphysics (Overview)

  • Limits to theoretical reason’s ability to determine answers to questions about the objects of its Ideas
  • Source of reason’s interest in moving beyond theoretical considerations
  • Immortality of the Soul as Practical Postulate
  • Existence of God as Practical Postulate
  • Metaphysics of Nature and Metaphysics of Morals

The Practical Extension of Reason and Traditional Metaphysics

The theoretical use of our reason leads us to ask questions about the things that we posit as grounds relative to natural phenomena. Some of these we can answer and others we cannot answer (either affirmatively or negatively):

Is the soul immaterial?

Yes, as the object of my inner sense, it is not a material thing or a body–materiality is a condition for the possibility of objects of outer sense (bodies), but it does not attach as a necessary condition to the object of inner sense (the soul).

Is the soul immortal?

I cannot determine that positively or negatively by appeal to any of the conditions for the possibility of empirical cognition. If I abstract from these, I can think that that the soul is a thing-in-itself that can continue to live without any connection to this particular body, or even without connection to any bodies whatsoever, but this is merely a speculative idea. If I assume that it does exist in this way, I have gone beyond a merely speculative consideration of some possibility to an unfounded judgement concerning real existence and matter of fact; this synthetic judgment could be false for all I know. If I take the unfounded synthetic judgement that the soul exists entirely independently of the body to be the expression of a fact, and then I deduce from this alleged fact that it cannot die, or that it cannot cease to exist altogether, through any natural process, I have gone even further away from the kinds of legitimate theoretical inference that my principles of reasoning support.

If we are tempted to answer this question in the affirmative, or we are tempted to assume that it is the case and then draw conclusions from there, it cannot be because of our interest in cognizing the truth from a merely theoretical perspective. The theoretical perspective is one from which we are equally averse to the risk of error as we are desirous of expanding our knowledge. Risk aversion should keep our theoretical reason in check here; we cannot know for certain by appeal to any legitimate principles of reasoning concerning matters of fact, so we should not assume it as a principle in theoretical contexts.

It must be, then, that the temptation to commit ourselves to some claim about real existence and matter of fact in this case stems from another interest of reason; namely, its practical interest in providing a secure guide for our pursuit of the various ends or goals that we have. Kant believes that the highest end or goal that we have is to achieve a perfect balance between our natural ends as animal beings and our moral end as rational beings:

As animals, we desire to have all our bodily needs met, to be free from bodily pain and mental anxiety, and to exercise our physical and mental capacities within the context of our (indeterminately long and full) animal life.

As rational beings, we desire to make ourselves worthy of that robust kind of happiness that i) we naturally pursue as animals, but ii) could not take to be completely and unequivocally good, if we did not live our lives in ways that would make it equally just for us to be able to enjoy this happiness.

Our overall practical interest, then, is in complete happiness in perfect proportion to, or in harmony with, complete virtue.

Can we get There from Here?

We begin our lives as incompletely virtuous, and there is no clear indication in our experience that we will be able to reach a state of complete virtue prior to the point in time at which our human body ceases to function.

Our practical interest in progressing to a state of being completely worthy of the happiness we desire, accordingly, provides us with an interest in postulating that our soul continues to function (in some way, we need not know how) beyond the point in time at which our body ceases to be a functional and animated unity. Since progress from some concrete and imperfect state towards some ideal point of completeness or perfection is always asymptotic, we also have an interest in thinking of our progress towards complete virtue as being endless progress; i.e., we are never there; there will always be room for improvement, but, thankfully, there will also always be opportunity to keep improving.

If we postulate the immortality of the soul in an effort to keep our hopes for continual moral progress alive, however, we will soon realize that we need to postulate something else in this same context; namely, the existence of God:

It is reasonable for us to hope for the opportunity to progress indefinitely towards complete virtue, only if it is also reasonable for us to presuppose that what justice demands concerning the harmony between virtue and happiness will, as a matter of fact, hold along the way in our pursuit. That is, if we do not postulate the perfect harmony between virtue and happiness, we cannot assume that our asymptotic approach to complete virtue (or complete moral worthiness to be happy) will also be an asymptotic approach to complete happiness. We are capable of counter-acting fleeting desires for particular sensible pleasures by appeal to our rational desire to be morally upright, but we are not capable of completely denying to ourselves any and all concern with our overall sensible state of well-being. Doing that would involve entirely overcoming or subverting our animal nature and, thus, ceasing to be human. A moral law or code of ethics that we absolutely had to follow here and now, even though we could positively rule out the possibility that following that law would also eventually lead to our happiness, would be a practical contradiction for human beings.

Accordingly, we have to presuppose, as a condition for the possibility of our moral agency, that the world (natural or otherwise) is ultimately governed by relations of justice in such a way that, by striving to be good (in the rational sense of that term = morally good), we will also be good (in the sensible or animal sense of that term = happy or content with our state of being).

The idea of a world-cause that ensures that there is a harmonious fit between the natural order of things and the moral order of things, or between what does happen as a matter of fact and what ought to happen as a matter of justice, is the most general idea of God that is shared by:

  1. Ancient philosophical traditions that distinguish themselves from the pagan polytheism of their political and social culture on this specific point concerning the world-cause (e.g., Platonic, Aristotelean, neo-Platonic, Epicurean, and Stoic schools of thinking)
  2. The ancient, medieval, and modern ethnic and social cultures that are associated with the holy texts of the three monotheistic religions in the West (i.e., Judaism, Christianity, and Islam)
  3. The ancient, medieval, and modern philosophical and theological traditions that seek to articulate independent rational grounds for belief in some of the basic principles of Western monotheism.

Accordingly, Kant provides an argument for the practical rationality of theistic belief that does not require any prior knowledge concerning the existence and characteristics of God. We are justified in postulating the existence of God, and the immortality of the soul, for the purposes of our own self-regulation as rational beings (who, importantly, do not stop being animals, simply in virtue of the innate intellectual capacities and the historically and culturally developed conditions for their exercise that we refer to as our rationality). A maximally coherent view of ourselves and of the natural and artificial (man-made) contexts in which we live and strive for knowledge, both for its own sake and for its practical utility, will, if Kant is right, be a theistic or a religious view. However, it will be one where we base our religious convictions and doctrines on our most basic moral commitments (to universal justice and to the freedom and dignity of all human beings) rather than basing our moral convictions and doctrines on basic and more narrowly religious commitments (e.g., concerning God’s favored people and the particular sacred texts that are expressive of God’s will for mankind).

The kind of metaphysics we are engaged in when we base religious convictions on moral commitments, is something that Kant calls the metaphysics of morals or pure practical philosophy, in order to distinguish it from the metaphysics of nature, or pure theoretical philosophy. It too, rests on synthetic a priori judgments that obtain legitimacy by appeal to conditions of real possibility. The real possibility we are primarily interested in, here, however, is not the real possibility of the phenomena we investigate in natural science (the realm of nature). It is, instead, the real possibility of a project of self-determination through our own rational capacities in ways that our actions will cohere with the actions of others who are doing the same, in precisely the way they would cohere, if we were all determined to act in the ways we do by the authority of a single, all-powerful, all-knowing, and all-loving legislator (a realm of freedom under moral laws, a kingdom of ends, or the realm of grace).


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