Sektionsredner

1.

There is much discussion about whether the human mind is a computer, whether a computer can have mental states, whether at all physical entities are computers (pan-computationalism), etc. These discussions presuppose a solution of the problem which objects in the world are computers - “problem of physical computation” (Shagrir 2006, 394ff). I propose to attack this problem via a clarification of what is a digital state.

2.

In a first approximation, being digital means being in a discrete state, a state that is strictly separated from another, not on a continuum. E.g. the digital (binary) states in a conventional computer, the states of a warning light, or the states in a game of chess.

It is characteristic of a digital mark that it can be realized several times: one can write the same word twice, even if one cannot make exactly the same mark on paper twice. Chess is a digital game because we can reproduce an earlier position precisely. (Haugeland 1985, 57).

3.

Every digital state is also on a continuum: Just looking at the physical distribution will not tell us anything. What is crucial is that a digital state is of a type. If it is of a type, then there can be multiple perfect realizations of it.

4.

It is helpful to differentiate at least three levels of description of a proposed candidate for being in digital or digital computational states: (a) physical level [realization], (b) syntactic [being of the type] and (c) semantic [representing something].

A digital computer works because it is constructed in such a fashion that some physi-cal states cause other physical states in a systematic way, and these physical states are also digital states on the syntactic level. (The physical states need not be of the same physical type; the semantic level may not be present at all.)

6.

If being of a type was the criterion for being digital, then everything would be in any number of digital states, depending on how it is described: this is too wide. Some-thing is digital because that is its particular function. My desk lamp is always in a digi-tal state, because being on/off is part of its function. The first letter of this sentence is in the digital state of being a “T” because that is its function – it is not an accidental orientation of ink or black pixels. The sun, on the other hand, is not in a digital state at present, though it can be shining or not shining at some place.

I conclude that we should say a state is digital if and only if it is a token of a type that serves a particular function.

7.

But: How can the account can be prevented from incorporating all too many states that are, intuitively, not digital states. For example, it will not only include the oil in-dicator lamp on my dashboard, but any lamp. What we explained so far is really not digital type, but type in general.

8.

So, which types are the digital ones? Let us look at some options:

Computational types – While it so happens that all digital states can be part of a digi-tal computational system, they do not have to be.

Types in a system - In specifying the function of a state, one is often required to take recourse to the system of which it is a part, in particular to the digital system (but not any system).

Pre-Defined types - Is pre-definition necessary, in order to make a system with digital states? And how are they pre-defined? The proposal is unnecessarily narrow, because it excludes digital states in systems that are not formally constructed. It would seem to show a priori that the human brain does not have digital states (except if a creator pre-defined them).

Syntactical/Formal types - Digital types are characteristically devoid of content; it really does not matter at all how they are realized, what properties they have, pro-vided that they are generally recognizable as being of the particular type. This aspect is probably best described by saying that digital types are syntactic types. A token of a syntactic type thus only contributes its being of that type to a larger syntactic system, nothing else. In particular, it cannot be said to have a meaning.

9.

The result seems to be that a digital type must be a syntactical type that is part of a syntactical system. One particular way to establish a syntactical system is to describe it in terms of algorithms, in other words as a computational system.

10.

Final questions:

Did I show here is that these questions deserve answers, not just decisions?

Does this analysis allow us to decide whether a given system, e.g. the human nervous system, involves digital states?

References

Haugeland, John (1985), Artificial intelligence: The very idea (Cambridge, Mass.: MIT Press).

Shagrir, Oron (2006), ‘Why we view the brain as a computer’, Synthese, 153 (3), 393-416.