Better Reasoning VIII: Acceptable Premises

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Previous posts in this series have mostly focused on the formal properties of deductive arguments, especially validity. However, another important feature that has an important effect upon whether or not we should be persuaded by an argument, is the truth, or otherwise of the premises. Regular readers of this series will recall that a valid deductive argument with true premises is sound and thus should be considered persuasive.

It turns out that figuring out the truth, or otherwise of premises is a little bit more tricky than one would originally realise. Consider an argument that uses the claim that ,

"The rate of acceleration due to Gravity is 9.8 meters per second squared."

Is such a premise true? Well, the answer is really 'sort of'. A more accurate value would be 9.81 meters per second squared. Does this mean that the premise is false? Again the answer is something like 'not exactly'. The problem here is that the precision that is appropriate will rather depend upon the context.

This is not the only kind of trouble that can arise when assessing the truth of premises. This fact was tacitly recognised by Ambrose Bierce in The Devil's Dictionary, where the following cynical definition of truth was offered,

"TRUTH, n. An ingenious compound of desirability and appearance. Discovery of truth is the sole purpose of philosophy, which is the most ancient occupation of the human mind and has a fair prospect of existing with increasing activity to the end of time."

Thus, assessing premises for 'truth' is perhaps not the best way to go. A good alternative is suggested by Trudy Govier in her A Practical Study of Argument, (6th Ed.), Wadsworth (2005). Govier suggests that premises should be assessed for 'Acceptability'. I will follow Govier's suggestion here.

Govier offers a number of tests that can be used to determine whether premises are acceptable, or not. If these tests are used, then a reasonable set of strategies for assessing premises result. It is worth emphasizing that it is really important that each premise must be assessed. It is also important that one think carefully to determine whether or not a particular premise really satisfies each test. Sometimes, it can even be helpful to construct a little argument to make sure. Also, just because a premise does not appear to satisfy one of these tests, is not sufficient to ensure that the premise is not acceptable. There is a separate set of unacceptability tests, that will be discussed later.

Govier's Acceptability Tests for Premises:

- Premises defended by cogent, or sound subarguments

If a premise is defended by a strong argument, then there is every reason to judge it acceptable. This should be obvious and uncontroversial. Of course, this puts the burden of acceptability back onto the strength of the subargument and the acceptability of the premises of the subargument.

- Premises defended elsewhere

It is often the case that premises will be defended in one place, and then used in another. For example this situation frequently arises in long texts. In some way, this condition is just a variant of the previous one. This kind of justification appears in academic writing through the use of references and citation to articles in refereed academic journals.

- Premises that are known a priori to be true

The idea behind a priori judgements is that there are some judgements that can be known to be true from the concepts alone, even prior to experience. To cite a couple of classic examples, if one knows that a particular object is a triangle, then one knows a priori that this object has three sides. Similarly, if one knows that a particular individual is a bachelor, then one knows a priori that the individual is unmarried. A priori judgements are not entirely uncontroversial. However, in the current context, this can still be a useful test for acceptability.

- Premises that are commonly known to be true

There is a class of premises that are not a priori truths, but nonetheless everyone knows to be true. For instance, most people will agree that, under the appropriate viewing and climatic conditions, the sky is blue. Similarly, most people will agree that, at least in temperate latitudes (the polar region present problems here), that there is less light at night than there is during the day.

- Premises that are supported by appropriate personal testimony

This condition is useful, but can be a bit tricky. Generally speaking, accepting premises using this test, should only be done if (i) the claim is not implausible, (ii) the source of the claim appears reliable, and (iii) the claim made does not go beyond a person's reasonable experience.

- Premises that are supported by a claim to proper authority

There are experts in the world. Generally speaking, their claims can be accepted. However, it is important to consider the extent to which the authority is a reasonable and credible person in the context. For instance, a professor may make a claim about an issue. However, if the issue is outside their specialised area of training and expertise, then the claim would not be acceptable.

- Premises that are provisionally acceptable

Sometime, in the context of a real argument, it is just not possible to determine whether a particular premise is true, in the context in which the argument is being offered. In such a case, it is not unreasonable to accept the premise only provisionally. For instance, people are often doing this kind of thing when they say things like 'for the sake of argument...'.

These tests are really quite useful when used in practice. However, having a bit of experience trying using these tests can make things easier. I recommend doing a few exercises. However, once a person has become reasonably familiar with these tests, determining which arguments to accept and which to reject becomes considerably easier. Next time, the ways that premises can be rendered unacceptable will be considered.

The CP

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Better Reasoning IX: Unacceptable Premises

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Just as there are a number of tests that can be used to determine when premises should be counted as being acceptable, there are also a number of ways that premises can be unacceptable (again, Govier is being followed here). As with acceptable premises, it is important to have a number of different tests. Also, it is important to ensure that a particular premise really does fail due to passing one of these tests. It is for this reason that it is sometimes useful to be able to give an argument as to why a particular premise is problematic.

There may be cases when a premise may appear to be intuitively unacceptable. However, when one considers the premise carefully, it may turn out to be less problematic than it initially appeared. There may even be cases where a particular premise does not seem to satisfy either an acceptability, or an unacceptability test. Although such cases are inherently problematic, this is the kind of case where the correct course of action is to consider the premise provisionally acceptable, pending further information.

Govier's Unacceptability tests for premises

- Premises that are easily refuted

If a premise is offered that can easily be shown to be false, then pretty obviously the premise will count as being unacceptable. A very effective method for doing this is to be able to offer a counter-example. It is also worth noting that the broader the claim made in a premise, the easier it is to counter in this manner. Thus, when considering arguments, it is always worth being on the look out for extremely broad premises. Now, let us consider an example. Suppose someone were to offer, as part of an argument, claims like,

(a) "All members of outlaw motorcycle club are illiterate", or
(b) "British people are all extremely proper and polite".

We could reject (a), as Ian 'Maz' Harris was a member of the British Hells Angels motorcycle club, yet had a Ph.D. It is not possible to get a Ph.D. if one is illiterate. We could similarly easily refute (b) by noting that Ozzy Osbourne is British. Osbourne is manifestly neither 'extremely proper', nor particularly 'polite'.

- Premises that are a priori falsehoods

There are cases where premises can simply be obviously false. Consider a case where someone appealed to the idea of a four sided triangle in an argument. The very idea of a four sided triangle is obviously nonsense, thus it would make no sense to accept a premise that appealed to such a notion. Other cases can be more subtle, however. Consider the case of an argument which rested upon the following premise,

"Anything which restricts freedom should not be passed into law."

We have seen something similar to this in this series before, when discussing enthymemes. On the face of it, this premise might seem vaguely plausible, if one was to think about all the rights and freedoms that are guaranteed by various nations. However, a little reflection shows that such a premise is problematic. This is because it is the very nature of laws, that they restrict freedom. My 'freedom' to drive too fast, for example, is restricted by speed limit laws.

There is another type of case which also follows under this test. If two premises explicitly contradict one another, then they should both be rejected (unless one is obviously true and the other obviously false). Consider, the following argument,

(1) Sentence (2) is false,
(2) Sentence (1) is true,
Therefore,
(3) The nothingness negates itself.

It turns out that together, sentences (1) and (2) form an instance of a famous philosophical puzzle known as The Liar's Paradox. It is pretty clear that these two sentences are problematic and as such should be judged unacceptable. There is an interesting point to note though, it turns out that the conclusion (3) actually follows validly from the two premises! This is due to the definition of validity. To put the matter simply. given the contradictory nature of the premises, it is never going to be possible for the premises to be true and the conclusion false, thus the argument is valid.

- Premises that contain implicit inconsistencies, or are problematically vague or ambiguous

Sometimes premises can be implicitly inconsistent with one another. Such cases are subtle and take some practice is detecting. However, suppose someone is giving an argument about the negative effects of a proposed trade policy. Supposed in one premise it is assumed that trade is going to increase, but in another that trade would decrease, both allegedly bringing about negative effects. In such a case, we would once again be justified in claiming that the premises were unacceptable.

Ambiguity can also be problematic and render a premise unacceptable. Consider for example the following rather silly claim that I spotted on a blog (a tragically bad one) some time ago,

"Academic feminists and not feminists."

This claim is somewhat odd. After all, a tabby cat is still a cat. What seems to be going on here is that the author intends the second use of the term 'feminists' to mean something rather different than the usual meaning, that is invoked by the first use of the term. It is pretty clear that this claim is basically incoherent and thus the premise should be ruled as unacceptable. Analogous difficulties can arrive when premises are irredeemably vague.

- Premises that are as dubious as the conclusions they support

Recall that the conclusions of arguments are usually controversial, surprising, or counter-intuitive. If an argument rests upon premises that are as dubious as the conclusions they purport to support, such premises should also be rejected as unacceptable. This situation is illustrated by the following argument,

"Since his alleged death, many people have reported sighting Elvis Presley in a variety of locations and situations in the continental United States. As the well-known aphorism has it 'There is no smoke without fire', so there are grounds for believing that Elvis Presley is still alive and well and living amongst us."

The conclusion here, that 'Elvis Presley is alive and well and living amongst us', is just a little surprising. However, the fact that people claim that they have seen Elvis is equally surprising (after all, they could be confusing Elvis impersonators for the real thing). Thus, the claim about Elvis sightings should be deemed unacceptable under this test.

- Premises that beg the question

If an argument tries to argue for a conclusion, by assuming the conclusion, then this too would render the argument problematic. This is handled by deeming the premise that encodes the conclusion as unacceptable. For example if someone attempted to argue,

"Orange is green, therefore orange is green."

we are unlikely to be too impressed. It is worth noting though that few cases are as blatant as this. A more subtle case, which is more like a real world example might be something like,

"It is unfair to raise our taxes, therefore it is unjust to do so."

There is in fact a very famous argument for the existence of God that suffers from just this kind of problem. It is known as the Ontological argument, originally proposed by Anselm. There are many versions of this argument. I will offer one of the simplest formulations here. Consider the following argument,

(1) God is 'that than which nothing greater can be conceived'.
(2) This conception of God implies existence (as an existing thing is greater than an equal thing which does not exist),
Therefore,
(3) God is that which cannot be conceived not to exist.

This is a classic case of a question begging argument. The fact that the conception of God specified in (1), is stipulated to imply existence in (2),just begs the question. This is pretty obviously objectionable.

When assessing a deductive argument, it is important to check whether the argument is valid. If the argument is valid, then it is next important to check the acceptability of the premises. In order for a premise to count as acceptable, it must pass one of the acceptability tests, discussed earlier. If a premise appears not to pass any of the acceptability tests, then the premise should be checked against the unacceptability tests. Only when a premise satisfies an acceptability, or an unacceptability tests, can we determine whether or not the arguments is sound. These are a powerful set of tools. However, they take a little practice to get the hang of applying in real world contexts. This is the reason why practicing these skills is extremely important.

The CP

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