At this point, I would like to elaborate more on Hume’s theory of mind and the origin of ideas as that would clarify why this example is so damaging to Hume’s system. As stated before, Hume’s project can be put into a general label of empiricism, which is a belief that all knowledge comes from experience. Much of his line of argument resembles that of Locke’s, another prominent empiricist. Hume even borrowed Locke’s key terminology to a certain extent, with terms like ideas and impressions. Locke believes that ideas are whatever the mind perceives in itself, or is in the immediate object of perception, thought, or understanding, as when one perceives, thinks, or understands, the ideas are before the mind. This limits all ideas to be originated from experience (perception), and also shows the connection between thought and perception and their interchangeable nature. The ideas can be divided into ideas of sensation (touch, smell, sight, etc.) and ideas of reflection (fear, happiness, sadness, etc.), which can then be separated further into simple and complex ideas, where complex ideas are derived from simple ones.
Hume follows this line of argument with some modifications. He claims he ‘restores’ the term ideas to its original sense by classifying the objects the mind is perceiving as perceptions, not directly as ideas as Locke have used, and from perceptions he then distinguished them into impressions and ideas, where they differ in degree, as impressions are more vivid and forceful before the mind, such when sees a colour, and the ideas are more faint, such when one thinks of a colour after having the impressions of it.
Hume then makes the distinction of simple and complex ideas, and by introspection, Hume demonstrates that one can think of any simple ideas and then find corresponding simple impressions that are exact copies of each other, and one can do this with any conceivable simple ideas. Complex ideas are different in that they are composites of simple ideas.
And with this experiment in introspection, Hume then postulates his first thesis, “… That all our simple ideas in their first appearance are deriv’d from simple impressions, which are correspondent to them, and which they exactly represent.” We may call this the Copy Principle, as it simply states that every simple idea is a copy of a corresponding impression.
One of the most important components of this thesis is the fact that it’s a genetic one in that it shows the origin of ideas as following from impressions – as impressions to be the cause of ideas. Again, this is proved by the constant conjunction of simple impressions preceding simple ideas, which one can do to every simple idea one may have. Another support Hume gives is that of a man born defective of certain perceptive organs, hence, missing certain impressions (e.g. sight or sound), one would not have any ideas of those corresponded with the impressions, for it is evident that deaf people also have great trouble speaking. The genetic component is important in that they validate the empiricism doctrine on the reliance of experience.
Anyhow, now we can see how the problem seems to defeat the purpose of this thesis. Moreover, a counter example, from a logical standpoint, one counter example is sufficient to turn an argument invalid. So why did Hume not deal with this problem?
We may try to take it as Hume claimed the problem to be – a singular case where it is not worth investing time on. Being a singular case, one may have to take the argument in closer inspection. Hume states explicitly that the man in question may have enjoyed the sights for thirty years and perfectly well acquainted with all the possible colours except one, and that may be the attempt by him to restrict this to some specific scenario. It is implicitly embedded in the counter example that the subject of this example must be well acquainted with all the colours, such that one can make up colours in one’s mind, much like how only musicians of a certain skill level can sight read music. Thus, it appeals to some amount of ‘experience’ such that one may be bound to experience, habits, or personal background. Yet, when given further consideration, this seems to be invalid as well, as these restrictions do not seem to hold. As far as experience go, a child who does not know what ‘turquoise’ mean does not necessarily have an idea of the colour ‘turquoise’.
So this case is certainly not an exceptional case and Hume had not dealt with it satisfactorily. Yet, Humean scholars have tried to find solutions for this problem and some even disregard it as a problem altogether.
Firstly, the first objection to this counter argument is that there is no way to test whether the person in question does in fact have an idea of the missing shade of blue before seeing the missing shade or not. There is a great difference between being able to spot a missing spot in a complete spectrum of blue, and being able to produce an idea of the shade of blue without first encountering the impression of it. If ones sees a constant change in shade from, let’s say blue-0 where it is darkest to blue-255 where it is the lightest shade, then if there is one shade of blue missing, it would be quite noticeable as the mind notices the jump in gradual and constant change, but it does not follow that one could create an idea of that missing shade. To test this is also impossible, as if one is to reproduce colour, it still does not follow that he produces the idea since he would only be mixing the existing colours to brighter shades, and thus, after finishing mixing the colour, one then has the idea of the colour following the impression. All other ways of testing is equally futile because they all involve exposing the subject to the missing impression one way or another.
Alternatively, if we look at the thesis again, and instead of taking it as a genetic form of the argument that Hume meant it to be, and instead, modifies it slightly to a more analytical empiricism form. Hume’s thesis on the theory of mind, upon closer inspection, can be taken as a form of meaning empiricism, in the sense that ideas to him are the same as different thoughts, which are different kinds of concepts, which is linked to when one understands something in a linguistic sense one is linking the word with the meaning, or the concepts associated to the word. Hence, if we think of the initial genetic content of the thesis, that impressions strictly precedes ideas, we may relax it slightly in favour of the analogy to meaning empiricism and forget its genetic form and instead formulate the following thesis: that all simple ideas must have corresponding conceivable and encounterable impressions. By doing this, we are no longer faced with the problem of the missing shade, since it is perfectly possible that the subject would be able to encounter this particular shade.
Lastly, from a personal view, I see the problem of the missing shade of blue as not a problem at all, but Hume’s mistake lies in classifying colours as simple ideas. It is true that the impressions of light blue might very well be different than dark blue, so to speak, but to use Hume’s method, it is possible to separate using our imagination the components ‘light’ and ‘dark’ from ‘blue’. Thus, it is the impression of ‘blueness’ which is a simple impression, combined with the impression of ‘light’ and ‘absent of light’ that combine to give this multitude of shades of colours. Take this example, suppose some neutral shade of blue, let’s number it blue 124, were put somewhere with light, you will be able to see blue 124. However, let’s say for some reason, the room becomes lighter, certainly, the shade of blue 124 would have changed to some lighter shade of perhaps blue 200. If we vary the light in the room from darkest to lightest, it is then possible to observe from the darkest to the lightest shade of blue likewise. One may argue that the colour can be calibrated to some objective criteria, perhaps the ratio of pigments of colour blue of some sort, yet, that does not matter since all that matters to Hume is indeed only impression. Furthermore, using this example, we can also say that perhaps the subject of the experiment may have in fact encountered the particular shade of blue sometime before without acknowledging it.
Conclusively, although Hume’s treatment of the missing shade of blue is very limited and very complacent, it is perhaps Hume’s own mistake for considering such example a ‘problem’, rather than the problem itself being a threat to his theory of origins of ideas.
