The Epistemology of Mental Illness Diagnosis I can see that the lands where Jumblies live would be *few*, sieves being so unbuoyant, but how did they make it *far*? Oh, perhaps they set out from far away and are still far away. Yes, that must be it. That would explain why a person never meets a Jumbly.
On the main question, we rely on conversations with others for all the measurements we make, not just assessing how we and others are feeling. Without being able to compare experiences with other people I would not know how to read a thermometer or what a thermometer is or whether the reading that I take is the same as or different from another person's reading or what kind of thing thermometers are presumed to measure. If we can reliably compare experiences of that sort and for that purpose, then I would not assume that we cannot compare experiences of mood, emotion, thought etc equally reliably and equally fallibly.