Other
The Mathematical Elements of Euclid
An extensive discussion of the Elements, which contains all the geometrical knowledge available in the Hellenistic period.
Friesian School
Fresian School: Kant and First Principles
This resource provides a good explanation of Kant's famous analytic-synthetic distinction. After explaining it, author critiques Kant's resolution of the problem of first principles.
Wolfram Research
Wolfram Math World: Postulate
This MathWorld site defines postulates, and explains how and where they are used in mathematics. The site has numerous links to related terms.