Thought experiments can provide deep insights, but a problem is that with many thought experiments are meant to prove what they actually already assume; or that the results follow from doubtful suppositions. Parfit’s Teletransport is a case in point. After having been teletransported Parfit’s wakes up and says “Examining my new body, I find no change at all.” (see my blog last week) With the help of this thought experiment Parfit reasons then that there is a psychological connectedness between Parfit on Earth and the teletransported Parfit on Mars. Leaving aside my criticism last week – which one could call “immanent” because it accepts the view that teletransport is a real possibility – I want to raise here a more fundamental point, namely that assuming the feasibility of such a teletransport is not right at all, unless it has been proven in practice. For I think that teletransport is not possible in the sense that Parfit wakes up on Mars and thinks that he is the person who just has been teletransported from Earth. One cannot correctly assume that it happens without any further reasoning or test. There is a simple argument against the idea: There is no intrinsic need to destroy Parfit on Earth when he is teletransported, and when we would omit Parfit’s destruction on Earth, there would be two Parfits thinking “I am Parfit”. Parfit on Earth is right, so Parfit on Mars cannot be, for he is not more than a copy. He remains a copy whether we destroy Parfit on Earth or whether we don’t. In my last blog I argued that Parfit’s reasoning was false, here I more fundamentally argue that Parfit’s thought experiment is false, since it is based on false assumptions.
To take yet another possibly false thought experiment, in his A Treatise Concerning Human Understanding David Hume wants to defend the thesis “that all our simple ideas in their first appearance are derived from simple impressions, which are correspondent to them, and which they exactly represent”. So first there is the observation and only then there is the idea. After having discussed two kinds of phenomena that support this thesis, Hume says: “There is however one contradictory phaenomenon, which may prove, that it is not absolutely impossible for ideas to go before their correspondent impressions.” For take this thought experiment: “Suppose ... a person to have enjoyed his sight for thirty years, and to have become perfectly well acquainted with colours of all kinds, excepting one particular shade of blue, for instance, which it never has been his fortune to meet with. Let all the different shades of that colour, except that single one, be placed before him, descending gradually from the deepest to the lightest; it is plain, that he will perceive a blank, where that shade is wanting, said will be sensible, that there is a greater distance in that place betwixt the contiguous colours, than in any other. Now I ask, whether it is possible for him, from his own imagination, to supply this deficiency, and raise up to himself the idea of that particular shade, though it had never been conveyed to him by his senses? I believe there are few but will be of opinion that he can; and this may serve as a proof, that the simple ideas are not always derived from the correspondent impressions”.
Now I think that this objection to Hume’s just mentioned thesis would be enough to falsify it. Not so for Hume. After having presented the thought experiment his conclusion is: “[T]he instance is so particular and singular, that it is scarce worth our observing, and does not merit that for it alone we should alter our general maxim.”
Be it as it may, is it right that the person in Hume’s case can supply “from his own imagination ... this deficiency, and raise up to himself the idea of that particular shade”, as Hume thinks? Helen De Cruz describes this experiment on the “Bored Panda” website and has added a drawing of several shades of blue with one missing plus a man in a blue sweater by way of illustration (see the link below). However, she adds: “Curiously though, when I presented this drawing to friends, they thought the man’s sweater was the missing shade of blue, but it isn’t! So perhaps it is not so easy to fill in the gap after all.” Maybe we cannot fill in the shade of blue simply by our imagination at all! What Hume assumes here in his mind needs to be proven in an experiment before we can accept it. As long as it hasn’t been performed, Hume’s blue shades case doesn’t refute his thesis. However, this thesis must be refuted for other reasons, which I’ll not discuss here.
- De Cruz, Helen, “8 Philosophical Thought Experiments That I Illustrated To Broaden Your Mind”, on website
- Hume, David, A Treatise Concerning Human Understanding, Book I, Sect.I, on websitehttp://www.gutenberg.org/files/4705/4705-h/4705-h.htm