“Between the philosopher's attitude towards the issue of reality and that of the mathematician there is this essential difference: for the philosopher the issue is paramount; the mathematician's love for reality is purely platonic.”

Original: (de) Ein Philosoph, der keine Beziehung zur Geometrie hat, ist nur ein halber Philosoph, und ein Mathematiker, der keine philosophische Ader hat, ist nur ein halber Mathematiker.

Gottlob Frege: Erkenntnisquellen der Mathematik und der mathematischen Naturwissenschaften, 1924/1925, submitted to Wissenschaftliche Grundlagen; posthumously published in: Frege, Gottlob: Nachgelassene Schriften und Wissenschaftlicher Briefwechsel. Felix Meiner Verlag, 1990, p. 293

"The Sad Fortunes of the Rev. Amos Barton" Ch. 4
Scenes of Clerical Life (1858)

I Want to be a Mathematician: An Automathography (1985)
Context: Mathematics is not a deductive science — that's a cliché. When you try to prove a theorem, you don't just list the hypotheses, and then start to reason. What you do is trial and error, experimentation, guesswork. You want to find out what the facts are, and what you do is in that respect similar to what a laboratory technician does. Possibly philosophers would look on us mathematicians the same way as we look on the technicians, if they dared.

The Man With the Blue Guitar (1937)

Turning physicists into quantum mechanics (2007)

The Age of Spiritual Machines: When Computers Exceed Human Intelligence (1999)

As quoted in "The Holocaust and Armenian Case: Highlighting the Main Differences" by Ibrahim Kaya http://www.turkishweekly.net/articles.php?id=61, in Turkish Weekly (10 April 2001)

Source: Ancillary Justice (2013), Chapter 4 (p. 54)

A Mathematician's Apology (1941)