{ 1 } - based on certain knowledge about sense data.
{ 2 } - uncertain.
{ 3 } - both of the above.
{ 4 } - neither of the above.

Foundationalists say that our empirical knowledge of the world is uncertain -- but is based on knowledge about sense data that is certain.

Austin rejects both ideas. He says that some of our empirical knowledge is certain; if we investigate a pig thoroughly enough, we can sometimes be sure that it's a pig. And sometimes we're uncertain about appearances; for example, we can be unsure of whether the shape is pink or red, or whether we see six dots or only five.