Narrow content and parameter proliferation

A centerpiece of Juhani Yli-Vakkuri and John Hawthorne's Narrow Content (OUP 2018) is the parameter proliferation argument. The authors consider a series of cleverly constructed cases of pairs of corresponding thoughts of qualitatively identical twins and argue that divergence in truth value for such thoughts forces the internalist to admit novel alethic parameters for semantic evaluation that are not independently motivated. I argue that the internalist will resist this argument by denying that such pairs of thoughts diverge in truth value. I then argue that the construal of content presupposed by the argument should be rejected or amended by the internalist on independent grounds. I end in a more diagnostic vein by considering why parameter proliferation might have seemed pressing for internalism to begin with.