Kant’s views on knowledge were strongly influenced by David Hume, whom he credited with having roused him from his ‘dogmatic slumbers’. Kant’s fundamental thesis is that the only possible objects of human knowledge are phenomena – the empirically observable objects of the world around us. ‘Nothing is really given us,’ he argued, ‘except perception and the empirical advance from this to other possible perceptions.’1 He is thus deeply suspicious of the claims of ‘rationalist’ philosophers of knowledge to describe a reality going wholly beyond the observable world. But he is equally critical of Locke’s thesis that knowledge arises from the ‘empty cabinet’ of the mind being furnished with sense impressions. As he puts it at the start of the extracts quoted below, ‘although all our knowledge begins with experience, it does not follow that it all arises out of experience’. According to Kant, the mind, in experiencing the world, necessarily interprets it or processes it in terms of a certain structure: it comes to the world already armed with ‘concepts of the understanding’. These concepts are described by Kant as a priori, meaning prior to, or independent of, experience. But Kant takes a crucially different route from previous innatists who had suggested that the mind was simply endowed (by God, as Descartes maintained, or from a previous existence, as Plato had it) with a range of nonempirical concepts and truths. Instead, Kant argues that all the concepts of the understanding are derived from certain fundamental categories which are presupposed by experience. Categories such as the categories of substance and causality are fundamental preconditions for our being able to experience the world at all. Kant thus offers a compromise between, or rather a synthesis of, empiricist and rationalist approaches to knowledge. Knowledge involves a kind of fusion of ‘intuitions’ (sensory representations) on the one hand, and the concepts of the understanding on the other. As he puts it below, in what has become a much-quoted slogan, ‘thoughts without content are empty, intuitions without concepts are blind’.
The distinction between pure and empirical knowledge
There can be no doubt that all our knowledge begins with experience. For how would our faculty of knowledge be awakened into action unless the objects affecting our senses produced representations, and also aroused the activity of our understanding to compare these representations? How, furthermore, could our knowledge be awakened unless our understanding, by combining or separating these representations, worked up the raw material of the sensible impressions into that knowledge of objects which is called experience? In the order of time, therefore, we have no knowledge antecedent to experience, and with experience all our knowledge begins.
But though all our knowledge begins with experience, it does not follow that it all arises out of experience. For it may well be that even our empirical knowledge is made up of what we receive through impressions, and of what our own faculty of knowledge supplies from itself (sensible impressions serving merely as the occasion). If our faculty of knowledge makes any such addition, it may be that we are not in a position to distinguish it from the raw material until with long-practised attention we have become skilled to do so.
This then is a question which at least calls for further examination, and does not permit any off-hand answer: is there any knowledge that is in this way independent of experience, and even of all impressions of the senses? Such knowledge is called a priori and is distinguished from the empirical, which has its sources a posteriori (that is, in experience).
The expression a priori does not however indicate precisely enough the full meaning of our question. For it has been customary to say, even of much knowledge that is derived from empirical sources, that we have it, or are capable of having it, a priori; what this is taken to mean is that we do not derive it immediately from experience, but from a universal rule – a rule which is itself borrowed from experience. Thus we might say of a man who undermined the foundations of a house that he might have known a priori that it would fall (that is, he need not have waited for the experience of its actually falling). But still he could not know this completely a priori. For he had first to learn through experience that bodies are heavy, and therefore fall when their supports are withdrawn.
In what follows, therefore, we shall understand by a priori knowledge not knowledge independent of this or that experience, but knowledge absolutely independent of all experience. Opposed to it is empirical knowledge, which is knowledge possible only a posteriori (that is, through experience). A priori modes of knowledge are called ‘pure’ when there is no admixture of anything empirical. Thus, for instance, the proposition ‘every change has a cause’, although an a priori proposition, is not a pure proposition, since ‘alteration’ is a concept which can be derived only from experience.
We are in possession of certain modes of a priori knowledge, and even the common understanding is never without them
What we require here is a criterion by which to distinguish with certainty between pure and empirical knowledge. Experience teaches us that a thing is so and so, but not that it cannot be otherwise. First, then, if we have a proposition which is thought of as necessary, it is an a priori judgement; and if in addition it is not derived from any proposition except one also having the validity of a necessary judgement, it is an absolutely a priori judgement. Secondly, experience never confers on its judgements true or strict, but only assumed and comparative universality, through induction.2
We can properly only say, therefore, that so far as we have hitherto observed there is no exception to this or that rule. If, then, a judgement is thought with strict universality, in such a manner that no exception is allowed as possible, it is not derived from experience, but is valid absolutely a priori. Empirical universality, by contrast, is only an arbitrary extension of a validity holding in most cases to one which holds in all (for instance, in the proposition ‘all bodies are heavy’). When, on the other hand, strict universality is essential to a judgement, this involves a special source of knowledge, namely a faculty of a priori knowledge. Necessity and strict universality are thus sure criteria of a priori knowledge, and are inseparable from each other …
Now it is easy to show that there are actually in human knowledge judgements which are necessary and in the strictest sense universal, and which are therefore pure a priori judgements. If an example from the sciences is asked for, we have only to look to any of the propositions of mathematics. If we seek an example from the understanding in its quite ordinary employment, the proposition ‘every change must have a cause’ will serve our purpose. Here the very concept of a cause so manifestly contains the concept of necessary connection with an effect, and of the strict universality of this rule, that the concept would be altogether lost if we tried to derive it (as Hume did)3 from a repeated association of that which happens with that which precedes … Even without appealing to such examples, it is possible to show that pure a priori principles are indispensable for the possibility of experience, and so to prove their existence a priori. For how could experience get its certainty if all the rules whereby it proceeds were always themselves empirical and therefore contingent? Such rules could hardly be regarded as first principles …
The idea of a transcendental logic
Our knowledge springs from two fundamental sources of the mind; the first is the capacity of receiving representations (the ability to receive impressions), the second is the power to know an object through these representations (spontaneity in the production of concepts). Through the first, an object is given to us; through the second, the object is thought in relation to that representation … Intuition and concepts constitute, therefore, the elements of all our knowledge, so that neither concepts without an intuition in some way corresponding to them, nor intuitions without concepts, can yield knowledge. Both may be either pure or empirical. When they contain sensation (which presupposes the actual presence of the object)