Pre-class: Kant

Nevertheless, from the throne of its moral legislative power, reason absolutely condemns war as a means of determining the right and makes seeking the state of peace a matter of unmitigated duty. (116)

This seems, to me, to be the essence of Kant's argument as to why a perpetual peace is not only possible, but, through progress of mankind, probable. The understanding of this quote (and Kant's theory of perpetual peace) is guided substantially by the understanding of Kant's views on the nature of duty.

For Kant, duty and morality are effectively twin hoods. He defines morality as "a science that teaches, not how we can be happy, but how we ought to become worthy of happiness" (63). He then paints duty as striving toward the highest good possible, which is "the purest morality throughout the world combined with such universal happiness as accords with it" (64). So, it is our obligation to strive after those things that are morally right (as defined by Reason)--the grand 'Ought' which is so often referenced. And, since humans are rational, they understand duty, and therefore are obligated to follow it--to shirk that duty would be irrational.

Also key in Kant's argument for perpetual peace is his argument that humans are progressing toward the highest good as history progresses. "I will thus permit myself to assume that since the human race's natural end is to make steady cultural progress, its moral end is to be conceived as progressing toward the better" (86). If humans were not progressing morally, there would be no chance of attaining a peaceful federation of states.
In light of this, then, the beginning quote and the unpacking of Kant's argument can be understood as follows (I hope I'm right (please comment judiciously if I'm not)): Because men are rational creatures that understand duty, and because mankind is progressing toward the highest good, when men gather together and participate in a republican government, they will inevitably fulfill their duty to pursue peace with other nations, and all republican nations will act in kind.

A couple of quick thoughts:

My Judeo-Christian worldview is drenched in the idea that, yes there is a highest good (sinlessness), and, yes, one should pursue that highest good, but ultimately one will not--indeed cannot--reach that highest good. Having Kant tell us that one actually can attain the highest good is a bit of a jolt.

Kant's qualifications for citizenship (p. 76) are a bit jarring to modern sensibilities.