Wikipedia places the philosophical root of the "Turing Test" with Descartes. Clearly Descartes is incredibly valuable in this regard, and also in regard to "cogito ergo sum", which can be applied to automata that perform calculations, as a basic condition in the overall philosophy of artificial intelligence.

But it seems to me the concept of the thresholds that constitute Turing Tests originates with Protagoras, who proposed that "Man is the measure of all things."

πάντων χρημάτων μέτρον ἐστὶν ἄνθρωπος, τῶν μὲν ὄντων ὡς ἔστιν, τῶν δὲ οὐκ ὄντων ὡς οὐκ ἔστιν.
Source: Sextus Empiricus, Adv. math. 7.60

Full quote may be translated as: "Of all things (used by man) the measure (of these things) is man: of the things that are, that they are, of the things that are not, that they are not."

(Apologies as I cannot find a direct link for the Greek online. I re-translated the first part of the proposition for clarity, but lifted the second part from Bostock, whose Ancient Greek is undoubtedly better than mine, because it is potentially ambiguous, even in the original, and Bostock's interpretation makes good use of that ambiguity.)

χρημάτων "things" is distinct from ὄντων "things", which is interpreted to mean Protagoras was speaking about things that man has a direct relationship to, such as property, tools, affairs and so forth. "A thing that one needs or uses" is listed in the LSJ.

Protagoras can unquestionably be extended to AI, which are tools.

  • What a great quote from Descartes. He exactly described the difference between weak and strong AI. en.wikipedia.org/wiki/Turing_test#Philosophical_background
    – user4894
    Mar 3, 2017 at 21:59
  • 2
    Protaqoras's quote is too generic to fit here. All he says is that "man" (as opposed to "gods", "objective reality", etc.) is the only judge of how things are. There is no relation here to machines or testing if they are intelligent (Protagoras could hardly even imagine what a "machine", in the relevant sense, might be). Descartes's quote, on the other hand, while still an anachronistic stretch, is at least to the point. And at least they already had mechanical arithmometers in his time.
    – Conifold
    Mar 4, 2017 at 0:42
  • Of course, Protagoras "point of view" can be used in any context, provided that we agree on the underlying relativism. Specifically, we can say that "intelligent" is a behaviour that looks like the human one; thus, a machine that mimicks relevant human behaviour can be said "intelligent". Thus: man is “the measure of all things, of the existence of the things that are and the non-existence of the things that are not”. Mar 4, 2017 at 10:40
  • Consider that the Turing test says more about the person using it than the test subject.
    – MmmHmm
    Mar 5, 2017 at 2:32

2 Answers 2


Protagoras's famous statement that "man is the measure of all things" has been variously related to relativism, Perspectivism, subjectivism, phenomenalism, anti-realism and skepticism. But not, as far as I know, to anything like the Turing Test (which is, to my mind, just a piece of common sense, hardly philosophical).

Here is Plato's Socrates, connecting Protagoras's statement to a kind of relativism reminiscent of Heraclitus, in Theaetetus 152a:

SOCRATES: Well, you have delivered yourself of a very important doctrine about knowledge; it is indeed the opinion of Protagoras, who has another way of expressing it. Man, he says, is the measure of all things, of the existence of things that are, and of the non-existence of things that are not:—You have read him?

THEAETETUS: O yes, again and again...

SOCRATES: A wise man is not likely to talk nonsense. Let us try to understand him...

SOCRATES: Now is the wind, regarded not in relation to us but absolutely, cold or not; or are we to say, with Protagoras, that the wind is cold to him who is cold, and not to him who is not?

THEAETETUS: I suppose the last...

SOCRATES: In the name of the Graces, what an almighty wise man Protagoras must have been! He spoke these things in a parable to the common herd, like you and me, but told the truth, 'his Truth,' (In allusion to a book of Protagoras' which bore this title.) in secret to his own disciples.

THEAETETUS: What do you mean, Socrates?

SOCRATES: I am about to speak of a high argument, in which all things are said to be relative; you cannot rightly call anything by any name, such as great or small, heavy or light, for the great will be small and the heavy light—there is no single thing or quality, but out of motion and change and admixture all things are becoming relatively to one another, which 'becoming' is by us incorrectly called being, but is really becoming, for nothing ever is, but all things are becoming.

Too little has been preserved from the pre-Socratics, so building upon them is anyway a speculative business. By the way, Epicurus was not a pre-Socratic. He was a born in 341 BC, that is 58 years after Socrates's death.

  • Thanks for weighing in! I was careful to mention "pre-Socratic and early philosophers" because my pursuit is not restricted to Protagoras. (That said, the current definition I'm finding for pre-Socratic is schools of thought not influenced by Socrates, and so Protagoras is currently listed on Wikipedia as a pre-Socratic.) I should also note that my current pursuit is mathematical representation of fundamental ideas may have application in Artificial Intelligence. Turing test is interesting because it is so subjective, but nonetheless, a threshold.
    – DukeZhou
    Mar 6, 2017 at 22:56

The article puts the root of the question of AI with Descartes. The root of the Turing Test is Turing. It is a radical departure from all previous accounts of the problem, ignoring the philosophical roots applied to it by everyone before him. The Turing Test is a renunciation of the root this idea has in Descartes.

If it is in the spirit of any philosopher, it would be someone like William James or John Dewey. You can see Pragmatism, natural language philosophy and even other naturalisms like Quine's and Searle's as proceeding from Protagoras, if you really want to, but it is an odd stretch.

You could apply that same ultimate root to approaches as far apart as Bentham's, Hume's and Lyotard's, and it would not be false, but it would not be productive. After all, what do those ultimately have in common that is not better explained by their witness of the rapid ascent of a modern scientific sensibility?

If their commonality goes back as, Whitehead seems to trace it in "Science and the Modern World", to the Europe's experience of intellectual simplification through the 17th and 18th centuries, it can no longer be productively traced onward to Protagoras, as he was not a major source in that era. In fact, the entire era saw a marked departure from caring about ancient roots.

  • Thank you for the thoughtful response! My approach my be deemed "applied semiotics in a mathematical context", so modern philosophy is far beyond the current scope. Right now I'm looking at ideas similar to "The way up and the way down are the same" as +1 = -1. This is true, for instance, in a modulo system such as base 2, where 0+1=1 and 1+1=0.
    – DukeZhou
    Mar 6, 2017 at 23:04

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .