For a friend:

“The problem of how a judgment can be synthetic and a priori, then, presents itself to Kant as the problem of how two concepts, neither of which includes the other, can be connected in a way which does not rest upon past experience and is not vulnerable to future experience.”

Page 23 of ‘Kant’s Analytic‘ by Jonathan Bennett.

On Locke at the Stanford Encyclopedia Of Philosophy:

‘Some philosophers before Locke had suggested that it would be good to find the limits of the Understanding, but what Locke does is to carry out this project in detail. In the four books of the Essay Locke considers the sources and nature of human knowledge. Book I argues that we have no innate knowledge. (In this he resembles Berkeley and Hume, and differs from Descartes and Leibniz.) So, at birth, the human mind is a sort of blank slate on which experience writes.’

On Charles Sanders Peirce.  Full entry here:

The previous point must be tempered with the fact that Peirce increasingly became a philosopher with broad and deep sympathies for both transcendental idealism and absolute idealism. His Kantian affinities are simpler and easier to understand than his Hegelian leanings. Having rejected a great deal in Kant, Peirce nevertheless shared with Charles Renouvier the view that Kant’s (quasi-)concept of the Ding an sich can play no role whatsoever in philosophy or in science other than the role that Kant ultimately assigned to it, viz. the role of a Grenzbegriff: a boundary-concept, or, perhaps a bit more accurately, a limiting concept. A supposed “reality” that is “outside” of every logical possibility of empirical or logical interaction with “it” can play no direct role in the sciences. Science can deal only with phenomena, that is to say, only with what can “appear” somehow in experience. All scientific concepts must somehow be traceable back to phenomenological roots. Thus, even when Peirce calls himself a “realist” or is called by others a “realist,” it must be kept in mind that Peirce was always a realist of the Kantian “empirical” sort and not a Kantian “transcendental realist.” His realism is similar to what Hilary Putnam has called “internal realism.” (As was said, Peirce was also a realist in quite another sense of he word: he was a realist or an anti-nominalist in the medieval sense.)