2 th - century theories of perception Reflection on whether mind-independent objects are the objects of perception is also present in the phenomenological tradition According to both Edmund Husserl and Maurice Merleau-Ponty, what we perceive appears to exist independently of our own existence In a line of reasoning that resembles considerations of perspectival variation, but that reaches different conclusions, Husserl and MerleauPonty argue that the mind-independence of the objects of perception is given by the fact that we can take multiple perspectives on the objects It is evident in the fact that taking different perspectives changes the way the objects look (Husserl 1900/1; Merleau-Ponty 1945) A similar conclusion concerning mind-independence is reached by more recent work on the phenomenology of other modalities Tactile experience, for example, delivers an appearance of something ‘external’ and mind-independent insofar as in touching something we experience the limit of our own body (Condillac 1947; Smith 2002; Strawson 1958) Thesis (b) of sense-data theory, according to which sense-data have the properties that they appear to us to have, is, like thesis (a), a problematic thesis, and it is sometimes credited with the introduction in philosophy of qualia – or qualitative properties present in experience This is not quite right, however American philosophers had already introduced the term ‘qualia’ somewhat independently of sense-data theory Charles Peirce used the term in relation to sense perception in 1866, and C I Lewis later used it in discussing the conceptual status of perception (Crane 2000; Lewis 1929; Peirce 1866/1931) Thesis (b) is a tacit presupposition of the argument from illusion According to the argument, when one perceptually experiences something, there must be something that one stands in the relation of perceiving to, and this something must have the properties which it seems to the perceiver to have For example, if it now looks to me as though there is a white expanse before me as I look at a wall, then an actual white expanse must exist, be sensed by me and have the properties I perceive it to have This is true even if I am misperceiving or hallucinating a wall And the property of being white, the reasoning goes, must be a non-physical property in this case This is because nothing in the environment, or in my head, is white when I am hallucinating a white wall Experienced properties like ‘being white’ are examples of qualia Although there are different senses of the term ‘qualia’ in contemporary philosophy, we can work with the idea that a quale is a qualitative property present in perceptual experience (Crane 2000 and this volume, Tye 2013) Some take qualia to be properties of the objects of experience Some take them to be properties of the experiences themselves Typical examples of qualia are the color of something seen, the pitch of a heard sound and the smell of an odor Because qualia can be present in experiences when no property corresponds to them in the environment (or in one’s head), they are thought to pose a threat to physicalist accounts of the mind Due to its metaphysics of mysterious objects and properties, sense-data theory was mostly abandoned in the second half of the 20th century, when physicalism 107