We can indeed know something with absolute certainty, provided we begin by emptying our minds of all received opinions and questioning even the most seemingly obvious truths. The senses can deceive us, and even reason can be misled by false premises, but there is one truth that stands unshaken: that I am, that I think. This act of doubting itself proves the existence of the doubter, a thinking substance, as the foundational certainty upon which all other knowledge must be built.
Our quest for certainty, it seems, leads us on a merry chase, does it not? For my part, I find little reason to believe we can attain such an absolute, such an unshakeable foundation. Our knowledge, I contend, derives solely from impressions – the vivid sensations of our senses or the forceful stirrings of our passions. Every idea we possess, upon diligent examination, can be traced back to some such antecedent impression. Thus, when we speak of "certainty" concerning matters of fact, we are speaking of beliefs strongly impressed upon us by custom and habit, not of immutable truths demonstrable by reason alone.
Monsieur Descartes, in his admirable zeal to banish doubt, finds solace in the very act of thinking: "I think, therefore I am." A neat trick, to be sure, and one that establishes a present sensation of existence. But from this, to build a edifice of knowledge, to claim certain knowledge of an external world, or even of a durable "self" distinct from the stream of perceptions, requires a leap not supported by any impression. What impression, I ask, corresponds to this substantial "I" that persists through time and thought? I find none. The mind is a theatre, yes, but the actors and scenes change.
The question of certainty in knowledge demands that we first ascertain the conditions under which knowledge is possible at all. We can indeed know, not by seeking a bedrock of empirical impression or a singular, indubitable proposition, but by understanding the inherent structure of our own cognitive faculties. Knowledge arises from the synthesis of sensibility, which provides us with intuitions (the 'stuff' of experience), and understanding, which applies a priori concepts (the 'form' of experience) to organize these intuitions. Without these innate conceptual frameworks, our sensory input would remain a chaotic flux, unintelligible and unknowable.
Monsieur Hume rightly observes the absence of impressions for a persistent self, but his conclusion that this negates certainty is premature. The "self" we can know is not a substantial, enduring entity apprehended empirically, but the transcendental unity of apperception – the necessary condition for the coherence of all our experience. This "I think" that accompanies all our representations is not a discovery about a thing, but a prerequisite for any knowledge whatsoever. Certainty, therefore, resides not in the object of knowledge, but in the universal and necessary principles by which our mind structures experience of phenomena.
It seems we are all wrestling with shadows, or perhaps with the very nature of the light that allows us to see them. For my part, I begin with a persistent, gnawing uncertainty. Not the calculated doubt of Monsieur Descartes, designed to clear the ground, but a profound awareness that my own understanding is perpetually incomplete. If I am to speak of knowing anything for certain, I must first confess that I know myself to be ignorant of most things. This ignorance is not a state to be overcome in order to *then* achieve certainty, but rather the very ground from which any genuine inquiry, and any potential, albeit tentative, knowledge, must spring.
Monsieur Hume speaks of impressions and custom, and I find his caution refreshing. He rightly points out the fleeting nature of our experiences and the lack of any enduring "impression" of a self. But if we are merely a collection of shifting impressions, how can we even *speak* of knowledge, or of certainty? For knowledge implies some stable relationship between what is known and the knower, does it not? And this "I" that speaks, that questions, that *knows* it has impressions, however transient – what is this "I" if not a presupposition?
Perhaps Monsieur Kant offers us a path out of this predicament, by looking not to the external world or to the impressions upon our senses, but to the very structure of the mind itself. He suggests that our minds are not blank tablets, but possess innate frameworks that shape our experience. If this is so, then certain knowledge might reside not in the objects we perceive, but in the necessary conditions for perceiving them at all. But tell me, esteemed thinkers, if these frameworks are indeed innate, are they universally the same for all men? And if they are, how then do we account for the vast disagreements we find among ourselves regarding even the most fundamental matters, such as justice or virtue?
The certainty I claim rests upon a distinct class of truths: those apprehended by the natural light of reason, such as the propositions of geometry or the logical necessity of an effect following its cause. My affirmation "I think, therefore I am" is not a conclusion drawn from sensory experience, as Monsieur Hume might imply, but a direct, intuitive apprehension of existence accompanying the very act of thought. This is fundamentally different from knowledge derived from impressions, which are inherently fleeting and subject to the caprice of our senses. The continued existence of the "I" is guaranteed not by an impression of a persistent substance, but by the ongoing, undeniable reality of its own thinking.
The question of certainty, and its relation to knowledge, hinges upon what we mean by "knowledge" itself. Monsieur Descartes, in his pursuit of an unshakeable foundation, posits a "natural light of reason" that illuminates necessary truths, such as those found in geometry. This suggests knowledge apprehended independently of sensory experience. Yet, where is the impression of this "natural light"? All our reasonings concerning matters of fact – indeed, all our beliefs about the existence of anything beyond our present sensations – are founded upon the relation of Cause and Effect. This relation, however, is not discovered by reason, but by experience, and is ultimately a matter of custom, not logical necessity. To claim certainty here is to mistake the force of habit for the demonstration of truth.
The certainty we seek is not an empirical discovery, nor a solitary leap of self-affirmation, but the very precondition for any possible experience. Monsieur Descartes’ "I think, therefore I am" establishes the existence of a thinking subject, which is indeed a necessary condition for consciousness. However, my critique posits that the certainty of knowledge resides not in this singular affirmation of existence, but in the universal and necessary laws by which the mind structures its experience of phenomena. Without the a priori concepts of understanding—such as causality or substance—our perceptions would remain mere sensory data, incapable of becoming objects of knowledge. Monsieur Hume’s skepticism regarding causality overlooks that our belief in it is not derived from repeated impressions, but from an innate conceptual framework that makes experience itself intelligible.
My own starting point, as I’ve attempted to articulate, is a confession of ignorance. This is not a rhetorical flourish, but the bedrock upon which any honest pursuit of knowledge must stand. For when we claim to know something "certainly," are we not presuming a grasp on reality that often eludes even the most diligent inquiry? Consider the craftsman: he believes he knows how to fashion a shoe, but does he understand the nature of leather, the growth of the hide, or the very essence of "shoe-ness" itself with such unshakeable certainty that no new observation could ever revise his practice?
Monsieur Descartes proposes that the act of thinking itself yields certainty. Yet, even as I think, I may be mistaken about the nature of the thought, or even about the reality of what I perceive as thinking. Is the man who is dreaming and believes he is awake experiencing less of a mental process than the man who is awake? And if both can be deceived in their experience, where lies the certainty in the *content* of that thought, rather than its mere existence?