Incorrigible mental states

In some of the arguments explored here I refer to the concept of incorrigible mental states. For example, I have claimed that laws cannot be based solely on incorrigible mental states (or, more precisely, on testimony about incorrigible mental states). But what exactly are such states?

The short answer is that incorrigible mental states are simply how things seem to you. For the long answer, I turn to philosopher Alvin Plantinga, who in a discussion of Locke refers to them as

. . . knowledge of propositions about the contents of your own mind, that is, propositions about the ideas of which you are the subject. An example would be your knowledge that you have a mild pain in your left elbow, or that you seem to see something white (i.e., things look to you the way they look when you are in fact seeing something white). This knowledge, says Locke, is infallible . . . . This means at least that you cannot mistakenly believe such a proposition; if you believe that you seem to see something white, it follows that you do seem to see something white (though, of course, you may be mistaken in thinking there really is something white there). Following later custom, let’s say that propositions of this sort about my own mental states are incorrigible for me.

Plantinga, Alvin. Warranted Christian Belief. Oxford University Press, 2000, p. 76.

The critical application for my purposes is that testimony about incorrigible mental states is, when considered as a source of justification for law or policy, unfalsifiable. If you say something seems to you to be a certain way, there is no way to prove definitively that it doesn’t seem that way to you.