Koellner is probably referring to Isaacson's paper, The reality of mathematics and the case of set theory. Isaacson appeals to Kreisel's argument that the second-order categoricity of set theory makes the continuum hypothesis a definite problem.

Koellner is probably referring to the paper

• Daniel Isaacson, The reality of mathematics and the case of set theory, in: Zsolt Novak and Andras Simonyi (eds), Truth, Reference, and Realism, Central European University Press, 2011. JSTOR (author pdf).

Isaacson appeals to Kreisel's argument that the second-order categoricity of set theory makes the continuum hypothesis a definite problem.

Koellner is probably referring to Isaacson's paper, The reality of mathematics and the case of set theory. Isaacson appeals to Kreisel's argument that the second-order categoricity of set theory makes the continuum hypothesis a definite problem.

Koellner is probably referring to Isaacson's paper, The reality of mathematics and the case of set theory. Isaacson appeals to Kreisel's argument that the second-order categoricity of set theory makes the continuum hypothesis a definite problem.