author of the Principia in 1687 to believe what the child Newton had believed in 1647.[61] To say that what is true to one man, is false to another--that what _was_ true to an individual as a child or as a youth, becomes false to him in his advanced years, is no real contradiction: though Plato, by omitting the qualifying words, presents it as if it were such. In every man's mind, the beliefs of the past have been modified or reversed, and the beliefs of the present are liable to be modified or reversed, by subsequent operative causes: by new supervening sensations, emotions, intellectual comparisons, authoritative teaching, or society, and so forth. [Footnote 59: Plato, Theætêt. p. 152 A. [Greek: Ou)kou=n ou(/tô pôs le/gei] (Protagoras) [Greek: ô(s oi(=a me\n e(/kasta e)moi\ phai/netai, toiau=ta me/n e)stin e)moi/--oi(=a de\ soi/, toiau=ta de\ au)= soi/.] 158 A. [Greek: ta\ phaino/mena e(ka/stô| tau=ta kai\ ei)=nai tou/tô| ô(=| phai/netai.] 160 C. [Greek: A)lêthê\s a)/ra e)moi\ ê( e)mê\ ai)/sthêsis; tê=s ga\r e)mê=s ou)si/as a)ei/ e)sti; kai\ e)gô\ kritê\s kata\ to\n Prôtago/ran tô=n te o)/ntôn e)moi/, ô(s e)/sti, kai\ tô=n mê\ o)/ntôn, ô(s ou)k e)/stin.] Comp. also pp. 166 D, 170 A, 177 C. Instead of saying [Greek: ai)/sthêsis] (in the passage just cited, p. 160 D), we might with quite equal truth put [Greek: A)lêthê\s a)/ra e)moi\ ê( e)mê\ _no/êsis_; tê=s ga\r e)mê=s ou)si/as a)ei/ e)/stin]. In this respect [Greek: ai)/sthêsis] and [Greek: no/êsis] are on a par. [Greek: No/êsis] is just as much relative to [Greek: o( noô=n] as [Greek: ai)/sthêsis] to [Greek: o( ai)sthano/menos].