Irrationalist is a wide term. It may be applied to mean "one without rationality", for their beliefs or ideas. Or, more precisely, it may mean someone who rejects some aspect of rationalism, variously defined. For example religious faith may be seen as, in part, a rejection of complete rationalism about the world; this would be contested by some religious thinkers, in that the rational is a debatable term. Additionally, some think it irrational for someone to believe that order and complexity can arise by chance. On the other hand, it might be considered irrationalist to buy a lottery ticket, on the basis that the expected value is negative.
In contemporary philosophy "irrationalism" is, inspired by Hindu and Buddhist philosophies, emerging into a new growing school of thought in which the importance of our intuitive capability is stressed. One such young philosopher, Robin Vermoesen (Belgium, 3 November 1978), states in his Dutch written book Rationaliteit is vals (translated: "Rationality is false") that every conscious is at the same time an individual being and total reality, thus as a consequence our rationalistic capabilities aren't enough if we truly want to understand reality in its truest form. For us to truly know reality we need to become it, we need to become our Self. He further states that there are four "knowledge relationships", (in growing order of intimacy: knowing, sensing, realizing and being) a being can experience, and all true knowledge of the Self, thus reality, must eventually grow into the most intimate of the four: being. Since rationalistic knowledge can bring us only knowing, it is, although a necessary tool, not enough to uncover reality. It needs to be balanced by other capabilities and framed in a patchwork that gives positive meaning to personal commitment.
Irrational thought was seen in Europe as part of the reaction against Continental rationalism. For example Hamann is sometimes classified as an irrationalist.
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