 Attempts to explicate acquaintance in non-epistemic terms fall into one of two categories. The traditional way to understand acquaintance is in terms of a containment relation between appearance beliefs and appearances, with the result that appearance beliefs entail their own truth. This is the indirect realist’s analogue of the world-involvement invoked by direct realists (above, sections  2.1.4,  2.3.3). Descartes (1641) held that appearance beliefs, like any belief about one’s own mental states, are infallible for this reason and thereby self-evident (and thus justified). Though some still endorse this view (McGrew 2003), most epistemologists deny that we are infallible in our self-attributions. A more modest claim is that only some appearance beliefs are infallible. David Chalmers (2003) argues that phenomenal qualities are literally elements or constituents of a special type of phenomenal concept (“direct phenomenal concepts”), and so introspective judgments that involve the application of such concepts cannot be mistaken.