> Kant was the original logical positivist.
>
> 1. First there were the rationalists, rebelling against religious dogma to
> put Reason on the intellectual throne.
> To them (i.e. Descartes), the senses delivered unsorted raw material, to be
> sorted by reason.
>
> 2. Then came the empiricists, proposing that there was no innate faculty
> like reason - there was nothing in the mind that had not before been in the
> senses. The mind was a blank slate, where experience wrote its lessons. The
> obvious flaw was immediately pointed out by Leibniz: There is nothing in the
> mind that had not been in the senses - except the mind itself.
>
> 3. Hume led empiricism ad absurdum by driving the program to its logical
> conclusion, eliminating most possibilities of knowledge, including -
> although he doesn't work this out himself - the premise of empiricism
> itself, i.e. the causal processes of sensation, which can no longer be
> upheld, since we cannot establish causality from experience.
>
> 4. Along comes Kant, awakened by Hume, picking up Leibniz' clue, and
> synthesizing rationalism and empiricism by asking: What is that slate, and
> how does it enable experience to write its lessons? What is the mind before
> it experiences? Is it really blank? Kant's conclusion is, as should be
> known, that it isn't - the rest in KdrV.
> However, he concluded that although we can create all sorts of concepts by
> reason alone, having these concepts doesn't constitute knowledge unless the
> concept is covered, in the banking sense, by a deposit of solid experience.
> And that's as far as we have come, although Wittgenstein, Russel, the Vienna
> Circle et al. have proposed refinements to the below excerpt of KdrV, and
> although certain authoresses even have suggested that this is not what Kant
> originally pointed out.
>
> Rivals include pragmatism in truth theory and constructivism in general
> epistemology, and few others, AFAIK.
>
> http://www.hkbu.edu.hk/~ppp/cpr/toc.html
> $22 The Category has no other Application in Knowledge than to Objects of
> Experience To think an object and to know an object are thus by no means the
> same thing. Knowledge involves two factors: first, the concept, through
> which an object in general is thought (the category); and secondly, the
> intuition (perception), through which it is given. For if no intuition
> (perception) could be given corresponding to the concept, the concept would
> still indeed be a thought, so far as its form is concerned, but would be
> without any object, and no knowledge of anything would be possible by means
> of it. So far as I could know, there would be nothing, and could be nothing,
> to which my thought could be applied. Now, as the Aesthetic has shown, the
> only intuition (perception) possible to us is sensible; consequently, the
> thought of an object in general, by means of a pure concept of
> understanding, can become knowledge for us only in so far as the concept is
> related to objects of the senses. Sensible intuition (perception) is either
> pure intuition (space and time) or empirical intuition (perception) of that
> which is immediately represented, through sensation, as actual in space and
> time. Through the determination of pure intuition we can acquire a priori
> knowledge of objects, as in mathematics, but only in regard to their form,
> as appearances; whether there can be things which must be intuited in this
> form, is still left undecided. Mathematical concepts are not, therefore, by
> themselves knowledge, except on the supposition that there are things which
> allow of being presented to us only in accordance with the form of that pure
> sensible intuition (perception). Now things in space and time are given only
> in so far as they are perceptions (that is, representations accompanied by
> sensation) -- therefore only through empirical representation. Consequently,
> the pure concepts of understanding, even when they are applied to a priori
> intuitions (percepts) , as in mathematics, yield knowledge only in so far as
> these intuitions (percepts) -- and therefore indirectly by their means the
> pure concepts also -- can be applied to empirical intuitions (percepts) .
> Even, therefore, with the aid of [pure] intuition, the categories do not
> afford us any knowledge of things; they do so only through their possible
> application to empirical intuition (perception). In other words, they serve
> only for the possibility of empirical knowledge; and such knowledge is what
> we entitle experience. Our conclusion is therefore this: the categories, as
> yielding knowledge of things, have no kind of application, save only in
> regard to things which may be objects of possible experience.
>
> $23 The above proposition is of the greatest importance; for it determines
> the limits of the employment of the pure concepts of understanding in regard
> to objects, just as the Transcendental Aesthetic determined the limits of
> the employment of the pure form of our sensible intuition (perception).
> Space and time, as conditions under which alone objects can possibly be
> given to us, are valid no further than for objects of the senses, and
> therefore only for experience. Beyond these limits they represent nothing;
> for they are only in the senses, and beyond them have no reality. The pure
> concepts of understanding are free from this limitation, and extend to
> objects of intuition (perception) in general, be the intuition (perception)
> like or unlike ours, if only it be sensible and not intellectual. But this
> extension of concepts beyond our sensible intuition (perception) is of no
> advantage to us. For as concepts of objects they are then empty, and do not
> even enable us to judge of their objects whether or not they are possible.
> They are mere forms of thought, without objective reality, since we have no
> intuition (perception) at hand to which the synthetic unity of apperception,
> which constitutes the whole content of these forms, could be applied, and in
> being so applied determine an object. Only our sensible and empirical
> intuition (perception) can give to them body and meaning. If we suppose an
> object of a non-sensible intuition to be given, we can indeed represent it
> through all the predicates which are implied in the presupposition that it
> has none of the characteristics proper to sensible intuition (perception);
> that it is not extended or in space, that its duration is not a time, that
> no change (succession of determinations in time) is to be met with in it,
> etc. But there is no proper knowledge if I thus merely indicate what the
> intuition (perception) of an object is not, without being able to say what
> it is that is contained in the intuition (perception). For I have not then
> shown that the object which I am thinking through my pure concept is even so
> much as possible, not being in a position to give any intuition (perception)
> corresponding to the concept, and being able only to say that our intuition
> (perception) is not applicable to it. But what has chiefly to be noted is
> this, that to such a something [in general] not a single one of all the
> categories could be applied. We could not, for instance, apply to it the
> concept of substance, meaning something which can exist as subject and never
> as mere predicate. For save in so far as empirical intuition (perception)
> provides the instance to which to apply it, I do not know whether there can
> be anything that corresponds to such a form of thought. But of this more
> hereafter.
>
> T