Explanations, Predictions, and Arguments

Contact: Dr. Jan Garrett

Last revised date: September 15, 2003

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In disassembling the complex argument stated immediately below for purposes of analysis, I shall use lower case letters to indicate statements. In the formal reconstruction at the end, I shall use numbered steps.

Consider this complex argument:

(a) A young man, Abe, who happens to be gay and does not deny it, has been assaulted by another young man, Bob, with no apparent provocation. (b) It is likely that Bob is prejudiced against gays. (c) This is the sort of thing we would expect persons with such a prejudice to do. (d) Anti-gay prejudice is a source of violence in our society. (e) We should address it as a community.

As it stands this is a weak argument. While it might suggest that Bob is prejudiced against gays, it does not establish it beyond a reasonable doubt. Of course, the reasoning could be strengthened by adding other premises and slight modifications of the wording. In any case, the point of introducing the argument here is not to defend or oppose its conclusion, stated in (e), but to clarify the common pattern of reasoning that it represents.

It is an argument based on a causal explanation, which in turn can be partly reworded as a hypothetical argument that reasons to a prediction. (A hypothetical argument is an argument of which a key premise is a supposition.)

The final part of the argument is added to the causal argument. Let's discuss and distinguish that part.

What is the final conclusion of this argument?

(e) We should address anti-gay prejudice as a community.

On what immediate premises (which could themselves be conclusions of simpler arguments) does this rest?

One of them is:

(d) Anti-gay prejudice is a source of violence in our society.

Another is implied but unstated:

(f) We should address sources of violence as a community.

The stated premise (d) is indeed an intermediate conclusion that rests on other premises. When we consider them we discover the explanation and the causal argument.

(d) clearly appeals to:

(g) Antigay prejudice is at least sometimes a cause of violence.
      (unstated but obviously intended)

(g) rests upon (h)

(h) There is at least one instance of assault caused by antigay prejudice.
      (unstated but obviously intended)

One case is not, of course, convincing proof of general causation, that many cases of violence are caused by antigay prejudice. But if combined with similar cases, it might contribute to such a proof.)

(h) rests directly upon

(i) The cause of Bob's assaulting Abe was Bob's antigay prejudice.

Now this claim is supported by the part of the passage that can be read either as an explanation or as an implicit hypothetical argument (argument that reasons from a hypothesis) leading to a prediction confirmed by undisputed fact. It is more or less spelled out in the first three sentences.

(a) A young man, Abe, who happens to be gay and does not deny it, has been assaulted by another young man, Bob, with no apparent provocation. (b) It is likely that Bob is prejudiced against gays. (c) This is the sort of thing we would expect persons with such a prejudice to do.

Note how this operates. It contains a hypothesis about Bob (b). It predicts behavior on the basis of that hypothesis (c). Then it finds that the prediction is confirmed by the fact. (c plus a)

Suppose
(j=b) Bob is strongly prejudiced against gays.

(k) A person strongly prejudiced against a class of persons is more likely than others to assault members of that class. (assumption, suggested by c)

We would conclude (a prediction) that it is likely that

(l) Bob might assault a gay person. (based logically on j and k)

The fact that Bob did assault a gay person (a, compare with l) is taken as confirmation of the truth of the supposition (j).

(The argument is far from persuasive as it stands, but might be made part of a more persuasive argument if we had more information.)

The point is that explanations can be rewritten as hypothetical arguments whose conclusion is a prediction that is confirmed by facts. When this happens, the hypothesis itself gains logical support.

Let us now renumber and formally reconstruct the argument under discussion. (Steps 9 and 10 illustrate just one way of getting from (8) to (11).)

(P=premise,
HP=hypothetical premise,
IC=intermediate conclusion,
A=assumption, which functions as a premise,
FC=final conclusion)

(1, P) A young man, Abe, who happens to be gay and does not deny it, has been assaulted by another young man, Bob, with no apparent provocation.

The explanation/causal argument from prediction covers steps (2)-(6):

(2, HP) Suppose Bob is strongly prejudiced against gays.

(3, A) A person strongly prejudiced against a class of persons is more likely than others to assault members of that class. (suggested by c)

(4, IC) Bob would be more likely than most to assault a gay person.
       (based on 2 and 3)

(5, IC) (4) is confirmed by (1)

(6, IC) (2) is probably true.
       (based on 5, which in turn rests on 1-4)

(7, A) When a hypothesis about a particular fact allows us to predict what happens, the fact gains credibility as the cause of what has been predicted.

(8, IC) Bob's assault was caused by his antigay prejudice.
      (based on steps 1-7)

(9, IC) There is at least one instance of assault caused by antigay prejudice. (based on 8)

(10, IC) Antigay prejudice is at least sometimes a cause of violence.
      (based on 9)

(11, IC) Antigay prejudice is a cause of violence. (based on 10)

(12, A) We should address causes of violence in our community.

(13, FC) We should address antigay prejudice in our community.
      (based on 11 and 12)