Mary Leng
Senior Lecturer

Complete our quick survey to help us improve staff profile pages



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

  • Director of Research.



My research has primarily been in the philosophy of mathematics and science, where I am particularly 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 (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. I thus defend a fictionalist approach to mathematical theories, falling under the Department's Fiction and Fictionality research theme.

More recently, I have become interested in overlaps in debates over realism and anti-realism in the philosophy of mathematics and in metaethics.  


  • debunking arguments in mathematics and ethics;
  • 'thick' concepts in mathematics and ethics.
  • explanation in mathematics and ethics.

Research group(s)

  • Mind and Reason
  • Practical Philosophy


In 2016-2017 I held a Leverhulme Research Fellowship on the topic 'Mathematics, Morals, and the Challenge to Physicalism'.


I have an ongoing collaboration with members of the Department of Logic and Philosophy of Science at the University of Santiago de Compestela, Spain.


I am interested in supervising students working in general philosophy of science and philosophy of mathematics, and in cosupervising projects in metaethics. 

External activities


Editorial duties

Media coverage

Hear me talking with Adrian Moore about the mathematics of the infinitely big as part of his Radio 4 series, A History of the Infinite

Mary Leng

Contact details

Dr Mary Leng
Senior Lecturer

Tel: 01904 323256



Foundations of Mathematics (3rd year)

Philosophy of Physics (3rd year)


Foundations of Mathematics (MA)

Other teaching

Modules taught previously include:

  • Paradoxes (yr 2)
  • Metaphysics (yr 1).