In “The Concept of Mind “ (1949), the philosopher Gilbert Ryle illustrates the concept of a category mistake. A foreign visitor to Oxford is shown colleges, libraries, playing field, museums, and so on. He says at the end, yes, but where is the University? It then has to be explained to him that the University is not some counterpart of the colleges he has seen, it is just the way in which what he has seen is organised. He was mistakenly allocating the University to the same category as that to which the other organisations belong.
Now substitute “John Smith” for Oxford University, and his data sets for the colleges and other university institutions. What are the interpretative and practical implications of looking at personal data like this?
On this reading, “John Smith” is the university without the university institutions. If there are personal data of the usual kind, it is only the peculiarity of that data set which establishes it as an individual’s data, and not the assumption that the data belongs to the proper name which has its own independent and identifying properties. That latter assumption reflects the category mistake made about John Smith, and leads to the belief you can achieve identification on the basis of a small amount of data plus a name.
An ID card is rather like the foreign visitor going home and wearing that souvenir T-shirt he bought with Oxford University on the front. The ID card starts with the wrong end first, the organising proper name; it is not so much function creep as data creep which is built into the ID concept, if you hang it around a proper name or unique identifier. You may think John Smith is an actual person, but where will you find him if he is like Oxford University? You will need lots of the personal data equivalents of those Oxford colleges.
Lastly, the Identity Thief. He is someone who, when he has the means (some of John Smith’s data) and the opportunity, invites someone else to play the category mistake game, to get someone else, on the basis of a small amount of data, to the point of making the category mistake. This also happens when John Smith is playing, only it doesn’t matter in the same way, because he is who he claims to be – something which is not established decisively by the security checks. The thief is playing a logical game, exploiting an everyday logical error involving a category mistake.