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Claudius Ptolemaeus (Greek: Κλαύδιος Πτολεμαῖος; ca. 100 – ca. 178), known in English as Ptolemy, was an ancient Greek geographer, astronomer, and astrologer who probably lived and worked in Alexandria, off the coast of Egypt.


  • We consider it a good principle to explain the phenomena by the simplest hypothesis possible.
    • Ptolemy attributed by James Franklin (2001) The Science of Conjecture: Evidence and Probability before Pascal. The Johns Hopkins University Press. Chap 9. p. 241


  • I know that I am mortal by nature and ephemeral, but when I trace at my pleasure the windings to and fro of the heavenly bodies, I no longer touch earth with my feet. I stand in the presence of Zeus himself and take my fill of ambrosia.
    • Penned in the margins.


  • πᾶν μὲν τὸ δυσέφικτον παρὰ τοῖς πολλοῖς εὐδιάβλητον ἔχει φύσιν
    • Everything that is hard to attain is easily assailed by the generality of men.
    • Book I, sec. 1
  • The length of life takes the leading place among inquiries about events following birth.
    • Book III, sec. 10
  • As material fortune is associated with the properties of the body, so honor belongs to those of the soul.
    • Book IV, sec. 1
  • There are three classes of friendship and enmity, since men are so disposed to one another either by preference or by need or through pleasure and pain.
    • Book IV, sec. 7

About Ptolemy[edit]

  • Ptolemy's Geography is the only book on cartography to have survived from the classical period and one of the most influential scientific works of all time.
    • J. Lennart Berggren, Alexander Jones, Ptolemy, (2001) Ptolemy's Geography: An Annotated Translation of the Theoretical Chapters
  • He left in his Optics, the earliest surviving table of angles of refraction from air to water. ...This table, quoted and requoted until modern times, has been admired... A closer glance at it, however, suggests that there was less experimentation involved in it than originally was thought, for the values of the angles of refraction form an arithmetic progression of second order... As in other portions of Greek Science, confidence in mathematics was here greater than that in the evidence of the senses, although the value corresponding to 60° agrees remarkably well with experience.
  • Ptolemy... against the champions of this or that cosmology of the heavens... had dared to claim that it is legitimate to interpret the facts of astronomy by the simplest geometrical scheme which will 'save the phenomena,' no matter whose metaphysics might be upset. His conception of the physical structure of the earth, however, prevented him from carrying through in earnest this principle of relativity, as his objections to the hypothesis that the earth moves amply show.

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