Parts 1, 2, and 3 of this series covered the importance of rules, logic, and definitions in thinking for the purpose of philosophizing. Indeed, for many people, philosophy and “logic” or “rationality” are often thought of as almost interchangeable. But when we read authors like Sartre, or Kierkegaard, or Nietzsche, we stumble across writing that seems profoundly illogical. Often, it appears to be just a collection of assertions and stories, with almost no logical glue connecting the overall view together. And yet, these are considered some of the more profound philosophers. When these authors are being so profoundly dismissive of logic and reason, how can other philosophers take them seriously?

Some examples:

Let us look each other in the face. We are Hyperboreans—we know well enough how remote our place is. “Neither by land nor by water will you find the road to the Hyperboreans”: even Pindar, in his day, knew that much about us. Beyond the North, beyond the ice, beyond death—our life, our happiness…. We have discovered that happiness; we know the way; we got our knowledge of it from thousands of years in the labyrinth. Who else has found it?—The man of today?—“I don’t know either the way out or the way in; I am whatever doesn’t know either the way out or the way in”—so sighs the man of today…. This is the sort of modernity that made us ill,—we sickened on lazy peace, cowardly compromise, the whole virtuous dirtiness of the modern Yea and Nay. This tolerance and largeur of the heart that “forgives” everything because it “understands” everything is a sirocco to us. Rather live amid the ice than among modern virtues and other such south-winds!… We were brave enough; we spared neither ourselves nor others; but we were a long time finding out where to direct our courage. We grew dismal; they called us fatalists. Our fate—it was the fulness, the tension, the storing up of powers. We thirsted for the lightnings and great deeds; we kept as far as possible from the happiness of the weakling, from “resignation”… There was thunder in our air; nature, as we embodied it, became overcast—for we had not yet found the way. The formula of our happiness: a Yea, a Nay, a straight line, a goal….

– Friedrich Nietzsche, The Antichrist

And,

There lived a man who, when a child, had heard the beautiful Bible story of how God tempted Abraham and how he stood the test, how he maintained his faith and, against his expectations, received his son back again. As this man grew older he read this same story with ever greater admiration; for now life had separated what had been united in the reverent simplicity of the child. And the older he grew, the more frequently his thoughts reverted to that story. His enthusiasm waxed stronger and stronger, and yet the story grew less and less clear to him. Finally he forgot everything else in thinking about it, and his soul contained but one wish, which was, to behold Abraham; and but one longing, which was, to have been witness to that event. His desire was, not to see the beautiful lands of the Orient, and not the splendor of the Promised Land, and not the reverent couple whose old age the Lord had blessed with children, and not the venerable figure of the aged patriarch, and not the god‑given vigorous youth of Isaac—it would have been the same to him if the event had come to pass on some barren heath. But his wish was, to have been with Abraham on the three days’ journey, when he rode with sorrow before him and with Isaac at his side.

– Søren Kierkegaard, Fear and Trembling

To understand this, we have to understand the purpose and nature of logic and rationality.

Logic and rationality are tools for pursuing a particular end. If I want a greener, lusher, more attractive lawn, I might use logical reasoning to move from this goal towards my desired aim — researching the best methods of fertilization, watering cycles, when to mow, etc. But the logic used to tell me how to get a green lawn does not tell me that I should have a green lawn.

David Hume famously identified this problem, which has become known in philosophy as the “is-ought” gap: one cannot logically deduce an obligation from a mere statement of fact:

In every system of morality, which I have hitherto met with, I have always remarked, that the author proceeds for some time in the ordinary way of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when of a sudden I am surprised to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not. This change is imperceptible; but is, however, of the last consequence. For as this ought, or ought not, expresses some new relation or affirmation, ’tis necessary that it should be observed and explained; and at the same time that a reason should be given, for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it. But as authors do not commonly use this precaution, I shall presume to recommend it to the readers; and am persuaded, that this small attention would subvert all the vulgar systems of morality, and let us see, that the distinction of vice and virtue is not founded merely on the relations of objects, nor is perceived by reason.

– David Hume, A Treatise on Human Nature (1739)

This is not to say that values cannot be discussed logically in some cases. IF I value beauty, and IF a green lawn is more beautiful than a brown and dead one, THEN it follows that I ought to cultivate a greener lawn.

But where is the logical argument that I should value beauty?

At some point, all worldviews become dependent upon a value or set of values which cannot be proven or defended logically. Philosopher and theologian Alvin Plantinga calls these beliefs “properly basic beliefs,” meaning that they are not dependent upon any other beliefs or premises.

Properly basic beliefs that are not founded on logic are necessary because without such beliefs, logic cannot get you anywhere. Logic is of no use without fundamental premises which are, themselves, not based in logic. Green lawns may be good because they are beautiful, but why is beauty good? For advancing the goodness of beauty, there really isn’t a logical argument.

Most philosophers begin with some shared assumptions, and try to use logic and reason in order to better understand the world from these presumed foundations — among the best examples are Aristotle and Descartes. But others — Nietzsche and Kierkegaard among them — try to grapple with those foundations themselves. They often have good “reasons,” but we must use the word “reasons” in quotation marks, because at that basic level, “reason” as ordinarily understood — logical thought — is simply not appropriate. How could one use logic to say that beauty is superior to ugliness? Or perhaps that ugliness is superior to beauty? Or that there is no true difference between the two?

When tackling questions such as these, philosophers may begin to sound like poets, or theologians, painting a picture with words which attempts to convey an insight or a point of view which challenges a basic presumption.

In short, logic is an excellent tool, but despite its strong association with philosophy, it is not the only tool in the philosopher’s toolbelt, nor is it even the best tool in certain circumstances. Philosophy is the love of wisdom, and in pursuit of wisdom, some ideas simply defy rational, logical investigation. But that does not mean that they defy investigation entirely.