Now the fact of my having the relevant experiences is beyond doubt. So we can be sure of the truth of sentences like 'experience of a table now', 'brown patch on the left of visual field' and so on. At last we have an incorrigible basis. If we add remembered similarity of experiences as an experienced relation between experiences, one could stipulate that significant sentences be built out of this solipsistic basis. This view of the basis was variously termed psychologism, phenomenalism and methodological solipsism, the idea being that we begin with what is epistemically secure, and work 'upwards', defining first statements about relations among 'sense data', then moving on to physical objects and so on.
Methodological solipsism is open to a number of objections.
A second and more telling problem concerns communicability. Under a phenomenalistic interpretation, basic statements report what is conclusively verifiable by experience, which must mean that 'There seems to be table in front of me' reports only my private experience . Secondly, as Carnap recognised, epistemological accounts of observation should take into account scientific investigations, and Carnap was impressed by Gestalt psychology. If, for instance, I find an empty bottle of a hallucinogen, and can find no table corresponding to an earlier experience, I might conclude that I have unwittingly partaken of the hallucinogen, and must re-interpret my earlier experience as reflecting a neural state that does not reliably indicate the presence of a table. If we want to keep afloat, we must rebuild the ship piecemeal, plank by plank.