Aksel Øijord: On the ontology of colours: Are colours heterogeneous or homogeneous? Are they two-dimensional or three-dimensional? Abstract My answer to the first question that is posed in the title of this thesis is that colours are homogeneous, which means each and every colour is only one in number. This means that colours are not heterogeneous, that is, they are not compounds or mixtures. For example: orange is often said to be red and yellow, and grey is often said to be white and black. In other words: orange and grey are both claimed to be heterogeneous. However, my conclusion that colours are homogeneous simply excludes that heterogeneity can be the case. My answer to the second question is that colours are two-dimensional, which means that colours stretch out in length and breadth, but not in depth. This conclusion gainsays naïve realistic conceptions about colours, for example that they can be objects like a piece of blue cobalt, or that there can be voluminous coloured light beams passing in three-dimensional space from a light source and, when they hit objects, mix with their colours. For example, one use to say that yellow and purple beams colour a landscape at sunset. The conclusion on two-dimensionality also gainsays the more sophisticated theory of identification of colours with brain events. That is, colours cannot be identified with brain events because the latter are three- dimensional while the former are two-dimensional. These two conclusions are drawn from three general propositions, which I call Basic Suppositions. The first says there is concomitance between colours and their extensions. This means that any colour has a certain extension and that this extension cannot be separated 1 from the colour itself. It follows that colours are homogeneous because if heterogeneous, like the contention on orange, the implication will be orange is twice its own extension, and this contradicts the first basic supposition. The second says that colours can only relate beside each other. This basic supposition gainsays naïve realistic conceptions which include that colours might exist behind each other and have different directions in three-dimensional space. The third says that only colours can limit colours, which means there can be no empty space or “clear air” between any two colours, i.e., it cannot be a blank or a gap between them, which is not a colour. In addition, my inquiry results in two other basic suppositions, namely that colours might be identical notwithstanding difference in figure, size or position, and that two or more different colours cannot be identical with one and the same colour. All these propositions will be clarified and defended in the discussion to follow. Method I proceed by naming colours. For example; this black is infield to which this white is outfield: X In this example, I denote the figure in question, the capital letter X, simply by naming it black. And also, I name its surroundings by the colour name white. That is, I am not trying to define particulars. And the common name colours refers to all particulars including white, black and grey. From there I detect their relational properties by using the substantival mode. The important thing to note is that when the substantival mode is used colour names function as subjects in sentences. This mode needs not only be used to characterizing colours by their positional relations, like the infield-outfield relation. Other characterizations are also possible. For example, a certain red in a white outfield may be a square. This means it has a certain relation to white, namely a square relation. But I can also characterize the same red by a sort of causal relation and for example contend it is a positive after image. The opposite is the adjectival mode which characterizes things or what is taken to be observable physical objects, by their colour properties, which is a naïve realistic approach. For example; this tomato is red, but that tomato is green. By this mode colour names function as predicates or adjectives in sentences. In some naïve realistic sciences, for example those of Goethe and Chevreul, whom I discuss in this thesis, the two modes are used together. For example, a contention is that red pigment mixes with yellow pigment into orange. Here red and yellow are used as adjectives respectively characterizing two different chemical materials, and orange characterizes the mix of those. However, a general contention might be that orange is a compound of red and yellow, and this latter contention conforms more clearly to the substantival mode. As I explain in General Introduction, section 1.5 below, the tradition from Hering to Hardin, does not, in the first place, bring causes into their determinations of particular 2 colours, and so, it is the substantival mode which is in use. However, determinations like orange is both red and yellow is some sort of defining colours by other colours, and gives reasons to believe in heterogeneity of colours. On the other hand, adherents of the tradition sometimes claim that such determination is purely psychological, i.e., without ontological implications. I discuss both options in the first section of General Introduction. In psychophysics, colours are characterized by their causes, and so also that discipline can be said to use the substantival mode. But these causes are theoretical entities, that is, they are in principle not observable. The talk is about differences of wavelengths of radiant energy, different purities of any one dominant wavelength, and differences of luminance which concerns intensity of radiant energy. These and purely neurophysiological causes are in themselves not colours and therefore not of concern to my exploration, though I give the principal explanatory structure considerable attention, especially in section 1 of General Introduction. My general contentions, i.e., the basic suppositions, are arrived at by observations and determinations of particular colour relations. And therefore, induction is fundamental to my method. From the basic suppositions I finally draw my conclusions. The structure of this thesis The text is divided in two, namely General Introduction and Chapters. General Introduction comprise the solutions to the problems discussed and the arguments for those solutions and is therefore not a short foreword, but a comprehensive text in where all the basic suppositions, except for number V, are formulated and defended. My reason for the divide is that the chapters relate to my findings and by that expand in orientation, addressing particular problems in colour philosophy. In section 1 of General Introduction, I address the contention that colours are heterogeneous, and argue that the terminologies both in naïve realistic sciences on colour, and in modern psychophysics, suggest that colours are judged heterogenous, and that this for apparent reasons can be a conviction about the ontology of colours. In section 2, I explain and defend my method and move into several themes related to the question if colours are homogeneous or heterogeneous, until I, in the last section, present and justify my argument in favour of colours’ homogeneity. In this run I also justify my general contention that colours can be identical notwithstanding difference in figure, size or position. In section 3.1, I first present my argument that colours are two-dimensional, and in sections 3.1.1 and 3.1.2, I give substantial justifications for the basic suppositions I use, respectively that colours can only relate beside each other and that only colours can limit colours. In this argumentation I address naïve realistic conceptions while paying them very much respect. In the last section 3.2, I consider most of psychologist Katz’s outlines of naïve realistic colour conceptions and conclude that those stand strong both in daily life and in science on colour, and that the belief in 3 colours’ two-dimensionality must be reserved for special colour conceptions, for example in psychophysics and eye-brain surgery. In the second part, which is divided into chapters, I try to show the relevance of my findings relating them to different themes. In chapter I, section 1, I present in brief all the basic suppositions. In section 2, I proceed to basic definitions, and in section 3, I present the main implications that can be drawn from the basic suppositions and definitions. I must confess that some definitions are not presented and defended in General introduction and that the implications are more than the two that answer the questions posed in the title of this thesis. However, I think the explanations I give in chapter I, are likely to be easily understood and accepted as sufficient justifications. In chapter II, I consider causal explanations in naïve realistic and realistic sciences. In relation to the former I gather conceptions from both Aristotle, Goethe and Chevreul. These are contrasted with the latter, represented by renaissance philosophy on colours, with focus on epiphenomenalism. I end the chapter by giving a brief outline of Eliminativism, a position defended both by Hardin and Arstila. In chapter III, I first discuss Hardin’s definition of unique colours, thereafter I repeat my critique on the lacking conceptual criteria for dividing colours into chromatic and achromatic. Then I present and discuss some theories of opponent colours within pigment colour systems. Further, I address some difficulties within colour systematics which arise from the detection of so-called forbidden colours. In the next sections I address the Swedish Natural Colour System and explain my reasons for not accepting that the use of the term natural is sufficiently counted for. In chapter IV, I discuss the problem of sorites series, which concerns degrees of likeness between colours. I refute the idea that two colours can be different while at the same time matching or being identical with a third colour.