The proper account, on the present conception is, of course, that the reference of 'yellowness' is ed by the description 'that (manifest) property of objects which causes them, under normal circumstances, to be seen as yellow (Le., to be sensed by certain visual impressions)'; 'yellow', of course, does not mean 'tends to produce such and such a sensation'; if we had had different neutral structures, if atmospheric conditions had been different, ifwe had been blind, and so on, then yellow objects would have done no such thing.