We should not argue with the blind man who maintained that sight was an illusion to which some abnormal people were subject. Therefore in speaking of… - Arthur Eddington

The problem of experiences is not limited to the interpretation of sense-impressions.

[P]erhaps there is something to be said for . The classic authorities tell us that he was only "doing a stunt," but I... think of him as a man who... brought to light a constructional defect in the flying-machines of his day. So too, in science, cautious Dædalus will apply his theories where he feels most confident... but by... excess caution their hidden weaknesses cannot be brought to light. Icarus will strain his theories to the breaking-point until the weak joints gape. ...But if he is not yet destined to reach the sun and solve for all time the riddle of its constitution, yet he may hope to learn from his journey some hints to build a better machine.

We used to think that if we knew one, we knew two, because one and one are two. We are finding that we must learn a great deal more about ‘and.