Mary Leng
Senior Lecturer



I have been a member of the Department of Philosophy at York since Spring 2012, having previously worked at Liverpool (as a Lecturer, 2006-2011) and Cambridge (as a Research Fellow, 2002-2006). I completed my PhD in philosophy at the University of Toronto, Canada, in 2002, and have held visiting research positions at the University of California at Irvine (2001) and the University of British Columbia (2003). As an undergraduate I studied Mathematics and Philosophy at Balliol College, Oxford (1993-1996).

Departmental roles

  • I am currently on funded research leave 2016-17

University roles

  • Member, University Research Committee (2015-present)



My research has primarily been in the philosophy of mathematics and science, where I am interested in the question of whether the role played by claims about mathematical objects (such as numbers) in our empirical scientific theories gives us reason to believe in mathematical objects. I have argued (particularly, in Mathematics and Reality (OUP, 2010)), that we can view the mathematical assumptions utilised by our empirical scientific theories as ‘useful fictions’, so that the use we make of mathematics in scientific theories does not support realism about mathematical objects.

More recently, I have become interested in the question of whether a mathematical fictionalist ought also to adopt moral fictionalism, or whether a combination of mathematical fictionalism and moral realism is a stable view.


  • ‘Mathematics, Morals, and the Challenge to Physicalism’ (2016-17). One year research project funded by the Leverhulme Trust.


I would be interested in supervising PhDs in the philosophy of mathematics and science, metaethics, and meta-metaphysics.

External activities


Editorial duties

Mary Leng

Contact details

Dr Mary Leng
Senior Lecturer

Tel: 01904 323256


Other teaching

Modules taught include:

  • Foundations of Mathematics (yr 3)
  • Philosophy of Physics (yr 3)
  • Paradoxes (yr 2)
  • Metaphysics (yr 1).