À Vontade do Freguês

Alan Turing, matemático inglês do séc. XX, teve uma enorme influência no desenvolvimento da Ciência dos Computadores. É dele a noção de "máquina de Turing", ou arquitectura de Turing. Possivelmente os leitores já terão usado um teste inverso de Turing, em que são instados a inserir dados caracteres numa caixa de texto, para provarem que são humanos e não bots ou afins. A Net está cheia de "CAPTCHAs" ou "Turing Numbers".

O teste inverso de Turing é - quem diria - a inversão do teste de Turing. Foi este último idealizado pelo inglês como forma de detectar se um computador, ou máquina, no sentido mais lato, para aferir a capacidade dessa máquina demonstrar, ou não, pensamento. A experiência funciona da seguinte maneira:

«a human judge engages in a natural language conversation with two other parties, one a human and the other a machine; if the judge cannot reliably tell which is which, then the machine is said to pass the test.» 

Não percam as objecções a este teste e as réplicas de Turing. Demonstram bem como nem tudo o que possamos querer, de facto é.

1. "’Heads in the Sand’ Objection: ‘The consequences of machines thinking would be too dreadful. Let us hope and believe that they cannot do so.’ " This objection is a fallacious appeal to consequences, confusing what should not be with what can or cannot be.
2. Mathematical Objections: This objection uses mathematical theorems, such as Gödel’s incompleteness theorem, to show that there are limits to what questions a computer system based on logic can answer. Turing suggests that humans are too often wrong themselves and pleased at the fallibility of a machine.
3. Mechanical Objections: A sufficiently fast machine with sufficiently large memory could be programmed with a large enough number of human questions and human responses to deliver a human answer to almost every question, and a vague random answer to the few questions not in its memory. This would simulate human response in a purely mechanical way. Psychologists have observed that most humans have a limited number of verbal responses.
4. Data Processing Objection: Machines process data bit by bit. Humans process data holistically. In this view, even if a machine appears human in every way, to treat it as human is to indulge in anthropomorphic thinking (recent advances in parallel computing and fuzzy logic based systems raise interesting questions regarding this specific objection).
5. Argument From Consciousness: This argument, suggested by Professor Geoffrey Jefferson in his 1949 Lister Oration, entitled, "The Mind of Mechanical Man," states that "not until a machine can write a sonnet or compose a concerto because of thoughts and emotions felt, and not by the chance fall of symbols, could we agree that machine equals brain." Turing replies by saying that we have no way of knowing that any individual other than ourselves experiences emotions, and that therefore we should accept the test. Also, few people actually can write a sonnet or compose a concerto, although are capable of feeling emotion.
6. Theological Objection: This states that thinking is a function of man’s immortal soul and therefore a machine could not think. Turing replies by saying that he sees no reason why it would not be possible for God to grant a computer a soul if He so wished.
7. Lady Lovelace Objection: One of the most famous objections, states that computers are incapable of originality. This is largely because, according to Ada Lovelace, machines are incapable of independent learning. Turing contradicts this by arguing that Lady Lovelace’s assumption was affected by the context from which she wrote, and if exposed to more contemporary scientific knowledge, it would become evident that the brain’s storage is quite similar to that of a computer. Turing further replies that computers could still surprise humans, in particular where the consequences of different facts are not immediately recognizable.
8. Informality of Behaviour: This argument states that any system governed by laws will be predictable and therefore not truly intelligent. Turing replies by stating that this is confusing laws of behaviour with general rules of conduct, and that if on a broad enough scale (such as is evident in man) machine behaviour would become increasingly difficult to predict. (Later research on recursive algorithms has found that, in any case, deterministic systems are capable of a chaotic diversity of behaviour.)^{[citation needed]}
9. Extra-sensory perception: Turing seems to suggest that there is evidence for extra-sensory perception. However, he feels that conditions could be created in which this would not affect the test and so may be disregarded. (No artigo citado)