While Chalmers leaves this particular argument open-ended, he seems to be suggesting that any physical law conceived of is metaphysically possible. The test of the degree of this possibility involves further defining the degree of conceivability. According to Chalmers, there are three sub-arguments for conceivability as entailing possibility: prima facie vs. ideal conceivability, positive vs. negative conceivability, and primary vs. secondary conceivability as entailing possibility.
Prima facie conceivability occurs when S is conceivable upon first appearance, or when there are no apparent contradictions to S. For example, it is prima facie conceivable that a table is made of wood if---at first glance---nothing apparently suggests otherwise. In order for S to be ideally conceivable, however, S has to pass certain tests that support it’s conceivability. In the case of the table, for example, one would have to further examine the table and still believe it to be made of wood for it to be ideally conceivable that it is made of wood. Obviously, ideal conceivability is superior to prima