He defined Type-0 thinking to be that concerned directly with the truth about the world. To find out whether astrology works, a Type-0 thinker might test its predictions against those made by rolling a die—and would inevitably conclude that it doesn't work. By contrast, Type-1 thinking is concerned with the truth about which beliefs are most advantageous to hold. A Type-1 thinker investigating astrology might first go to nightclubs acting as though he believes it—"Hey baby, what's your sign?"—and then go acting as though he doesn't believe it, so that he can calculate which belief is the more often smiled upon by Venus. We can also define Type-2 thinking—concerned with the truth about which beliefs about the truth about which beliefs are most advantageous to hold are most advantageous to hold—as well as Type-3, Type-4, and so on.
-- On self-delusion and limited rationality by Scott Aaronson