First degree formulas in quantified S5

  • Alasdair Urquhart University of Toronto


This note provides a proof that the formula L(Ex)( Fx & ~LFx) is not equivalent to any first degree formula in the context of the quantified version of the modal logic S5. This solves a problem posed by Max Cresswell.


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Author Biography

Alasdair Urquhart, University of Toronto

Professor Emeritus

Departments of Philosophy and Computer Science

How to Cite
URQUHART, Alasdair. First degree formulas in quantified S5. The Australasian Journal of Logic, [S.l.], v. 12, n. 5, july 2015. ISSN 1448-5052. Available at: <>. Date accessed: 02 july 2020. doi: