What is "Radical"?

That which is 'radical' is not based on empirical or evidentiary basis, but rather on relative differences between what is, and what is proposed. That is to say, that a radical political idea is not radical because it has no evidence to support it, but because it is so drastically different from the idea it is being proposed to replace.

Instead of radical, the word 'speculative' is better used. Socialism, in its pure theoretical form, is not radical for the United States (based on practice as it is now) but rather speculative. Similarly Libertarianism is not radical in the United States (based on the cultural mythology) but speculative.  These minute distinctions are of vital importance as so often in politics we see ideologies being wantonly labeled as 'radical' with no clarification as to what radical means.