Oil-paintings grow dark, frescoes fade, statues lose noses, hands and legs, architecture becomes totally or partially a ruin, the tradition of the execution of a piece of music is lost, the text of a poem is corrupted by bad copyists or bad printing. These are obvious instances of I the changes which daily occur in objects or physical stimuli. As regards psychological conditions, we will not dwell upon the cases of deafness or blindness, that is to say, upon the loss of entire orders of psychical impressions; these cases are secondary and of less importance compared with the fundamental, daily, inevitable and perpetual changes of the society around us and of the internal conditions of our individual life. The phonetic manifestations or words and verses of Dante's _Commedia_ must produce a very different impression on an Italian citizen engaged in the politics of the third Rome, from that experienced by a well-informed and intimate contemporary of the poet. The Madonna of Cimabue is still in the Church of Santa Maria Novella; but does she speak to the visitor of to-day as to the Florentines of the thirteenth century? Even though she were not also darkened by time, must we not suppose that the impression which she now produces is altogether different from that of former times? And even in the case of the same individual poet, will a poem composed by him in youth make the same impression upon him when he re-reads it in his old age, with psychic conditions altogether changed? [Sidenote: _Criticism of the distinction of signs into natural and conventional._]