A system of creating meaning and establishing justification whose premises remain open to rational criticism. This system typically operates in intuitive metphoric ways. As a system of reason they share the common characteristic of their openess to rational scrutiny and criticism, and hence the implication that they have survived rational criticism to present and remain reliable. --JakeSapiens03.01.07
{From reply #69 in the 
Unreason: a meme you need thread on the BBS}
Reason is a very sophisticated game of abstraction. The game pieces consists of bits of knowledge, variously known as propositions, statements or sentences. Some pieces describe the state of the world, e.g. "nine planets orbit the sun in our solar system". Some pieces describe the pieces used to describe the world (definitions are an example). Some pieces, called conditionals, describe the world as it could be. Some pieces called goals, describe the worlds as it should be.
Other pieces, the ones that make this the game of Reason, describe how to manipulate all the pieces in a valid way. These rules are also part of the game, which makes it self-referential like the game of Nomic. The rules are used by the players to tell how pieces can relate to each other, and how to generate new pieces or remove existing pieces from the game.
All the pieces, in addition to encoding some knowledge, have an associated truth value that reflects our confidence in the veracity, validity, probability, etc. of the piece. The truth value is used for consistency checks and generating new pieces. Truth values also change when related pieces change.
The pieces are arranged in a network of implications. The rules define what the implications are, a simple example is: if there is a piece X with truth value t, then there is another piece not-X with truth value (1-t). When you are playing the game, you can use that rule to create the 2nd piece (if it doesn't already exist) or alter the truth values of the pieces when one of them changes.
Now there is much(!) more to be said on this topic. I am just clarifying these ideas in my own mind as a direct result of this thread (thanks, garyrob). Hopefully this sketch will give you some idea about how I see Reason being much larger than the rules of inference. Sort of like how there is vastly more to the game of chess than the rules of how the pieces can move. But even to compare it to chess is an understatement. The whole field of mathematics is a subset of Reason. The whole enterprise of science is a subset of Reason.