Kenneth Dover, The Greeks
, 3rd ed. (Austin: University of Texas Press, 1989), p. 124:
Greek historians were never afraid to use their own judgement. They were willing to say 'I don't know', to speculate about the motives of the people they described, and to qualify their opinions on occasion by 'perhaps' and 'probably'. It is the appearance of words like 'perhaps' which marks the beginning of true historical writing.
S.C. Woodhouse, English-Greek Dictionary: A Vocabulary of the Attic Language
(London: George Routledge & Sons, 1910), p. 606:
seem to occur more often in Thucydides than in Herodotus.