Grounding Sensible Qualities

This conference is part of a larger research project, funded by a grant from the New Directions in the Study of Mind Project at Cambridge University (http://www.newdirectionsproject.com). Our project begins with the natural thought that an adequate account of sense perception—perception of a sensible world—is only possible once we have a satisfactory understanding of the nature of sensible qualities themselves. We aim to investigate two paradigmatic qualities—colour and shape—and the relations they bear to the physical world and to the mind. Our project seeks to enrich the study of sense experience by incorporating insights from contemporary metaphysics, the history of philosophy, and empirical findings in physics and psychology.

I. Colour

During the Early Modern period, many philosophers, impressed by the discoveries of the Scientific Revolution, argued that colours must be mind-dependent - grounded in the mind, to put it in modern parlance. On such views, colours were either ideas in the mind (for Berkeley or Hume), or powers to cause experiences (for Descartes and Locke). More recently, however, this kind of subjectivist account of colour has fallen out of favor. Many philosophers now insist that sensible qualities are properties of ordinary medium-sized physical objects; that such physical objects retain their colours in the absence of any minds; and that, therefore, colours must be fully grounded in the external material world.

Despite the current popularity of the thesis that colours are mind-independent properties of material bodies, the traditional Early Modern view was not without its motivations. If we grant the pre-theoretically powerful intuition that we can become aware of essentially qualitative colours, sounds and tastes in hallucinations or in experiences of phosphenes or afterimages—experiences that lack any suitable material objects of awareness—we are naturally driven to the view that such qualitative properties cannot be grounded in the ordinary objects of the material world (for if they were, how could they be instantiated in the absence of their grounds?) and must instead be grounded in the mind.

Our methodological approach is to be inclusive of both sides of this debate. While philosophers have typically drawn a strict line between the kinds of properties—mass, charge, spin etc.—that inhere in material objects and the itches, pains and tickles that are by their nature dependent on our minds, we are interested in exploring the view that secondary qualities like colour straddle this ontological divide. This hypothesis receives prima facie support from the expansive range of entities to which we ordinarily attribute colours – a list that includes material bodies, lights, rainbows, phosphenes and after-images. In the background of these metaphysical investigations lies the question: Can an ontologically flexible view of colour give us a more satisfying account of colour perception?

II. Shape

While the Scientific Revolution of the Early Modern period led many philosophers to argue that colours were grounded in our awareness of them, no such challenge from Early Modern science threatened the naïve conception of shape properties as grounded in the physical world. But in the contemporary context, where Einsteinian relativity and quantum mechanics have both called into question the views of spatial properties endorsed by the Early Moderns, we can no longer see macroscopic shape properties as unproblematically grounded in the external world.

Faced with this challenge, one reaction would be to extend the Early Modern thesis of mind-dependence—the claim that sensible qualities like colours are grounded not in the world but in our minds—to shapes. A historical precedent for such a move can be found in Kant and his interpreters. Strawson (1966) suggests that the Euclidean shapes we encounter in experience are to be taken as features of phenomenal, rather than physical, space – as grounded in our minds’ cognitive architecture, rather than in the external world’s physical matter.

Such a view presupposes that the Euclidean space we fail to find in the contemporary description of the external world is instead present in our experience. But relocating Euclidean space in this way opens up another challenge, from a different branch of contemporary science: many results in perceptual psychology are taken to show that visual space is not in fact Euclidean. Empirical data suggest that subjects’ judgments about key geometrical features of “visual objects”—such as whether two arrays of lights form parallel lines—fail to conform to Euclid’s postulates. (See Luneberg (1947); Hatfield (2003); Masrour (2015)).

Combined, the challenges from contemporary physics and psychology would seem to leave no suitable grounds for the Euclidean shape properties traditionally thought to characterize the objects of our perceptual experience. We will investigate how these challenges might be addressed, and what implications our contemporary scientific worldview might have for theories of shape perception.