There are four main philosophical accounts of incommensurability/incomparability. Joseph Raz has argued that in cases of incomparability, no comparison applies. A second argument is more fundamental, and this rests on the possibility of incomparability. Not every partial order obeys the transitive law for incomparability. Like all incomparability graphs, trapezoid graphs are perfect. Semiorders generalize strict weak orderings, but do not assume transitivity of incomparability. An advantage of this account is that the various puzzles surrounding incomparability dissolve rather quickly. Bitolerance graphs are incomparability graphs of a bitolerance order. According to this view, apparent incomparability is merely ignorance. Comparability is denoted by the symbol formula 1, and incomparability by the symbol formula 2. Finally, a set of philosophers led by John Broome has argued that incomparability is vagueness. Incomparability has figured prominently in several philosophical debates concerning moral and rational action.