score:6
Yes, Catholics must believe in the historicity of Christ.
Is there some philosophical doctrine in Catholicism which does not require to believe in the historicity of Christ
No. This is the heresy of Modernism, whose philosophical foundation is agnosticism.
Pope St. Pius X condemned the following proposition as heretical in Lamentabili Sane (1907):
- It is permissible to grant that the Christ of history is far inferior to the Christ Who is the object of faith.
In Pope St. Pius X's encyclical Pascendi Dominici gregis (1907), he writes (§6):
…it is inferred [by the Modernists] that God can never be the direct object of science, and that, as regards history, He must not be considered as an historical subject.
See also Pascendi §§ 9-10, 16-17, and esp. 29-33, and passim.