Michael Jacovides

Locke’s porphyry argument at 2.8.19 of the Essay has not been properly appreciated. On my reconstruction, Locke argues from the premise that porphyry undergoes a mere Cambridge change of color in different lighting conditions to the conclusion that porphyry’s colors do not belong to it as it is in itself. I argue that his argument is not quite sound, but it would be if Locke chose a different stone, alexandrite. Examining his argument teaches us something about the relation between explanatory qualities and real alterations and something about the ways that colors inhere in bodies

'If a person can think of an F, then that person has come into causal contact with an F in the right way' is a premise in an obvious reconstruction of Putnam's argument that we are not brains in vats. 'If a person can think of an F, then that person has come into causal contact with an F or with something at least as good as an F' is the only controversial premise in Descartes' argument for the existence of God. Putnam's principle entails Descartes', which suggests that we should enquire after better versions of Putnam's proof. I present three variations and conclude that Putnam's semantic theory does not have anti-sceptical consequences. In contrast, given Descartes' cognitive situation, he was perfectly justified in accepting the soundness of his argument for the existence of God.