Internalism about truth holds that a belief's being true is a function of things internal to the mind of the believer. Coherentism and Spinoza's extreme rationalism are two kinds of internalisms about truth. Spinoza's argument in the Treatise for the Emendation of the Intellect is basically:
- If internalism is not correct, truth is not worth having.
- Truth is worth having.
- Therefore, internalism is correct.
For (1) to be at all plausible, we need "worth having" to mean intrinsically worth having, and that makes (2) less plausible, though I think (2) remains true. But I deny (1), with or without the qualification, because some things can be intrinsically worth having without being internal or intrinsic to the person. Thus, it is worth having one's friends do well, even though my friends' doing well is not internal or intrinsic to me. Of course my friends' doing well tends to affect me. But not always: my friend could be doing well in my absence, without any contact we me, and that directly makes me better off.
One can also run the argument in terms of knowledge instead of truth. (I think for Spinoza the two come to the same thing! Spinoza thinks knowledge is true belief, but he has high standards for what counts as true belief—beliefs not justified up to Cartesian standards need not apply.)