I have argued that a connection between fact and belief that guarantees truth is a necessary condition for knowledge. I have further argued that the connection must be causal in nature, at least in the attenuated sense of being a k-causal connection. If my claim is correct, then we do not have knowledge of platonic objects. I have discussed difficulties for sustaining these claims in the face of various objections and counterexamples. In this chapter, I argue that a global causal requirement is not the only basis for a causal objection to platonism. By a "global" requirement, I mean one that applies to all knowledge. My challenge to the platonist will be to ask how we can know that platonic objects, as such, exist. I shift the focus of the debate away from causal constraints on knowledge in general and towards causal constraints on existential knowledge, by which I mean, knowledge that certain entities exist.¹