Deductive and plausible thinking: the problem of ‘gay gangsters’

Yesterday a friend sent me a link to this news story:

HARARE – There are real fears that the ugly infighting within President Robert Mugabe’s Zanu PF party has now come perilously close to degenerating into a fatal war that could see opponents organising hits against each other.

This emerged after motormouth Hurungwe West legislator Temba Mliswa convened a media conference in Harare yesterday where he made sensational claims as the fallout from the party’s deadly factional and succession battle escalates.

Among Mliswa’s myriad bombshell allegations was his below-the-belt claim that politburo members and Cabinet ministers Jonathan Moyo and Saviour Kasukuwere were “gay gangsters who have hijacked the ruling party”.

The fiery Zanu PF Mashonaland West provincial chairperson’s acerbic attack on his party colleagues follows recent State media accusations that he was allegedly a Central Intelligence Agency (CIA) mole.

His broadside yesterday also came in the wake of worsening factional fights in the party that have seen deputy Foreign Affairs minister Christopher Mutsvangwa taking the unprecedented step of questioning Vice President Joice Mujuru’s war credentials.

“The question… is whether the party has become a party of gay gangsters because it is not a secret that Kasukuwere and Jonathan Moyo are close,” Mliswa said.

“It is a whole syndicate of gay people, otherwise what would you be doing shopping in New York with another man, leaving your wife behind and the man is excited about having to go shopping with you?” Mliswa asked rhetorically, adding that this was the reason why suspended Sunday Mail Editor Edmund Kudzayi, “a 29 year-old man without a wife” had been hired by Moyo.

Let’s unpack Mliswa’s thinking on the homosexuality question (I won’t touch the ‘gangster’ aspect as Mliswa provides no evidence for this claim at all):

  1. If two men are homosexual, then one of the things that they will do is go shopping without female company.
  2. Moyo and Kusukuwere went shopping in New York without female company.
  3. Therefore, the two men are homosexual.

If this strikes you as being something less than Champagne Logic, then take a bow. Regardless of the correctness or otherwise of the first premise, this reasoning commits the Fallacy of the Consequent. Take it away, Susan:

It hardly needs to be emphasised that it is fallacious to conclude, from the affirmation that the consequent is true, that the antecedent can likewise be asserted to be true. The same consequent may have many different antecedents … [I]t is fallacious owing to the fact that the conclusion goes beyond the evidence. [Thinking to Some Purpose, pp.160,161]

So Mliswa’s deductive logic is less than golden. However, had he paid attention in his philosophy classes, then he might have been more careful and said ‘It is plausible that Moyo and Kusukuwere are gay. Just look at their behaviour in New York, going shopping without female companions.’

This is because, although we can’t conclude from Mliswa’s argument that the pair is gay, it is possible that his conclusion is plausible, so long as we accept his premise.

Plausible reasoning says that, although our conclusion may not necessarily follow from what we observe, what we observe may actually make that conclusion plausible, to a greater or lesser degree.

I’ll hand over to Edwin Jaynes, whose unfinished magnum opus, Probability Theory: The Logic of Science, explored plausible reasoning in depth.

Suppose some dark night a policeman walks down a street, apparently deserted. Suddenly he hears a burglar alarm, looks across the street, and sees a jewelry store with a broken window. Then a gentleman wearing a mask comes crawling out through the broken window, carrying a bag which turns out to be full of expensive jewelry. The policeman doesn’t hesitate at all in deciding that this gentleman is dishonest. But by what reasoning process does he arrive at this conclusion? Let us first take a leisurely look at the general nature of such problems.

A moment’s thought makes it clear that our policeman’s conclusion was not a logical deduction fro the evidence; for there may have been a perfectly innocent explanation for everything. It might be, for example that this gentleman was the owner of the jewelry store and he was coming home form a masquerade party, and didn’t have the key with him. However, just as he walked by his store, a passing truck threw a stone through the window, and he was only protecting his own property.

Now, while the policeman’s reasoning process was not logical deduction, we will grant that it had a certain degree of validity. The evidence did not make the gentleman’s dishonesty certain, but it did make it extremely plausible. This is an example of a king of reasoning in which we have all become more or less proficient, necessarily, long before studying mathematical theories. We are hardly able to get through one waking hour without facing some situation (e.g. will it rain or won’t it?) where we do not have enough information to permit deductive reasoning; but still we must decide immediately what to do.

In spite of its familiarity, the formation of plausible conclusions is a very subtle process. Although history records discussions of it extending over 24 centuries, probably nobody has ever produced an analysis of the process which anyone else finds completely satisfactory. In this work we will be able to report some useful and encouraging new progress, in which conflicting intuitive judgments are replaced by definite theorems, and ad hoc procedures are replaced by rules that are determined uniquely by some very elementary – and nearly inescapable – criteria of rationality.

All discussions of these questions start by giving examples of the contrast between deductive reasoning and plausible reasoning. As is generally credited to the Organon of Aristotle (fourth century BC) deductive reasoning (apodeixis) can be analyzed ultimately into the repeated application of two strong syllogisms;

if A is true, then B is true

A is true

therefore, B is true,

and its inverse:

if A is true, then B is true

B is false

therefore, A is false.

This is the kind of reasoning we would like to use all the time; but, as noted, in almost all the situations confronting us we do not have the right kind of information to allow this kind of reasoning. We fall back on weaker syllogisms (epagoge):

if A is true, then B is true

B is true

therefore, A becomes more plausible.

The evidence does not probe that A is true, but verification of one of its consequences does give us more confidence in A

Another weak syllogism, still using the same major premise, is

If A is true, then B is true

A is false

therefore, B becomes less plausible.

In this case, the evidence does not prove that B is false; but one of the possible reasons for its being true has been eliminated, and so we feel less confident about B. The reasoning of a scientist, by which he accepts or rejects his theories, consists almost entirely of syllogisms of the second and third kind.

Now, the reasoning of the policeman was not even of the above types. It is best described by a still weaker syllogism:

If A is true, then B becomes more plausible

B is true

therefore, A becomes more plausible.

But in spite of the apparent weakness of this argument, when stated abstractly in terms of A and B, we recognize that the policeman’s conclusion has a very strong convincing power. There is something which makes us believe that, in this particular case, his argument had almost the power of deductive reasoning.

These examples show that the brain, in doing plausible reasoning, not only decides whether something becomes more plausible or less plausible, but that it evaluates the degree of plausibility in some way … And the brain also makes use of old information as well as the specific new data of the problem …

Thus in our reasoning we depend very much on prior information to help us in evaluating the degree of plausibility in a new problem. This reasoning process goes on unconsciously, almost instantaneously, and we conceal how complicated it really is by calling it common sense.

The mathematician George Polya wrote three books about plausible reasoning, pointing out a wealth of interesting examples and showing that there are definite rules by which we do plausible reasoning.

Personally, I think Mliswa’s on shaky ground: I don’t think his conclusion is at all plausible. It’s just another tiresome smear, probably baseless, that he is using to attack his political enemies.

But it has given us a chance to explore the differences between deductive and plausible reasoning. And understanding is the first step in correct application.


About Stebbing Heuer

A person interested in exploring human perception, reasoning, judgement and deciding, and in promoting clear, effective thinking and the making of good decisions.
This entry was posted in Formal fallacies in reasoning, Reasoning and tagged , . Bookmark the permalink.

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