see a priori.
a term from the work of Isaiah Berlin (1907-97) which refers to the absence of external restraint. Having negative liberty means that one is free to act. However, one still may not be able to act because of a lack of capacity, power, or ability and this is where Berlin introduces the concept of 'positive liberty' which is the capacity to act as one would wish. For example, any school leaver is free to spend a gap year abroad, if they so wish - negative liberty - but it is probably only those with sufficient money, confidence, support, and physical health who are actually able to do this - positive liberty.
literally a 'belief in nothing', it is applied to a range of views, most notably materialism which, in denying that mind or spirit exists, rejects immortality or an after-life. It is also applied to politically or socially destructive behaviour.