1. Allaire, E. B. 1966. ‘The “tractatus”: nominalistic or realistic?’ in R. W. Beard and I. M. Copi (eds.), Essays on Wittgenstein's ‘Tractatus’, New York: Macmillan, pp. 189–194.
2. Anscombe, G. E. M. 1966. ‘Mr Copi on objects, properties and relations in the Tractatus’, in R. W. Beard and I. M. Copi (eds.), Essays on Wittgenstein's ‘Tractatus’, New York: Macmillan, pp. 187–188.
3. Copi, I. M. 1966. ‘Objects, properties and relations in the Tractatus’, in I. M. Copi and R. W. Beard (eds.), Essays on Wittgenstein's ‘Tractatus’, New York: Macmillan, pp. 167–186.