Suppose I tell a friend that the rose bush on my front porch is in bloom. If he wonders how I know such a thing, I might respond that I saw it as I left for work this morning. If pressed, I might invite my friend home so he can see the bush for himself. What is supposed to be served by my report of what I saw? It is supposed to provide justification for what I say by grounding it in what I see. But what does "grounding' mean here? My claim about the rose bush is a claim about an entity in the world, and I assume that looking at such an entity warrants the claim, that perceiving it underwrites the truth of what I say. Sceptics have often questioned this assumption, pointing out that perception can be deceptive in many ways; indeed, we may have no good reason for holding that any perception delivers the world as it is. When I make a judgement, the object about which I judge becomes a standard against which the judgement may be measured: if the object is as I say it is, then my judgement is true (i.e., does what it is supposed to do as this judgement); if not, not.