There are a great many of these and we will have time to consider only a few. They divide generally into two main types – fallacies of relevance, and fallacies of ambiguity.
Fallacies of Relevance
To prove the truth of a proposition, one must offer evidence that is relevant. Fallacies of relevance do not do this – however psychologically powerful they may be. A selection of the more common ones is given below.
Argumentum ad Baculum (appeal to force)
This is often used in politics. A lobbyist uses it when he reminds a politician that he (the lobbyist) represents thousands of voters in the politician’s constituency. This, of course, has no relevance to the legislation that he is trying to influence.
Argumentum ad Hominem (argument against the man)
This can take one of two forms – an abusive one and a circumstantial one.
The abusive form attempts to discredit a point of view by discrediting the person who holds it. But the character of the person holding the view entails nothing about the truth of that view. To argue that a politician’s arguments are false because he is being prosecuted for fiddling his expenses is to commit this fallacy. His arguments may be entirely valid – bad man though he may be.
This form of the fallacy pertains to the relationship between a person’s beliefs and his or her circumstances. For example, one may assert a certain contention on a clergyman because its denial would be incompatible with the scriptures.
Argumentum ad Ignorantiam (argument from ignorance)
This is straightforward enough. To assert that there are no such things as ghosts because you have never seen one is a good and simple example.
Argumentum ad Misericordiam (appeal to pity)
This is often used in courts of law when a defending counsel attempts (often very skilfully) to persuade a jury to find a defendant not guilty of doing something that he clearly has done because of the wretched circumstances of the defendant’s life.
Argumentum ad Populum (appeal to the people/gallery)
This is a favourite tool of the propagandist, the demagogue, and the advertiser; we get it almost daily from politicians. When a politician is opposing a change, he may express a suspicion of “new-fangled ideas” and praise the wisdom of the “existing order”. Or, if he is for it, he may be for “progress” and be opposed to “antiquated prejudice”. A user of this type of argument is essentially attempting to arouse the feelings and enthusiasms of a large number of people.
Argumentum ad Vericundiam (appeal to authority)
The appeal is to the feeling of respect people have for the famous in order to win assent for a particular conclusion. It is often used in advertising where a motor car manufacturer claims that, e.g., Lewis Hamilton drives a ….. It is also often used in debates about whether, e.g., God exists where an appeal is made to the view of a famous person.
The fallacy of applying a general rule to a particular case of which the “accidental” (the actual) circumstances make the rule inapplicable. Plato notes, in the Republic, that the general rule that one should pay one’s debts does not apply when one has borrowed weapons from a friend who was in his right mind at the time but when the time comes to return them the friend is not in his right mind.
Converse Accident (hasty generalisation)
For example, if one considers the effect of alcohol on those who drink to excess and concludes that all alcohol consumption is harmful, one commits this fallacy.
To mistake what is not the cause for the real cause and also to assume that an event is the cause of another simply because it precedes the later event. These actions are more common than you might think. An obvious example would be that of a witch doctor claiming that beating his drum makes the Sun reappear after an eclipse (even though he can remind people that every time his drum has been beaten during an eclipse the Sun reappears). This fallacy is often employed by people selling patent herbal medicines.
Petitio Principii (begging the question)
Assuming as a premiss for an argument, the conclusion one is trying to draw, is to commit this fallacy. Copi gives an example quoted from Whately as follows:
To allow every man unbounded freedom of speech must always be, on the whole, advantageous to the State; for it is highly conducive to the interests of the community that each individual should enjoy a liberty, perfectly unlimited, of expressing his sentiments.
The famous lawyer’s question “Have you stopped beating your wife?” is a good example. It is a question containing a presupposition – that the man of whom it was asked had been beating his wife – and does not therefore admit of a simple “yes” or “no” answer. It can be more subtle than this, e.g., “Where did you hide the evidence?”.
Ignoratio Elenchi (irrelevant conclusion)
For instance, when a particular proposal for housing legislation is under consideration, a politician rises to speak in favour of the bill and argues only that decent housing for all the people is desirable, he commits this fallacy. Few people would dispute his assertion but it is irrelevant to the proposal being considered (Will this proposal provide the decent housing?).
Fallacies of Ambiguity
These are arguments containing words or phrases that are ambiguous and in which the ambiguities change in meaning during the arguments.
Many words have more than one meaning. If these meanings are mixed in a logical argument, the fallacy of equivocation is committed. For instance,
The end of a thing is its perfection.
Death is the end of life.
Therefore death is the perfection of life.
Here the word end is used in two ways – first to mean something like goal and then to mean something like last event.
When premisses are formulated ambiguously because of their grammatical construction, an argument based on them is amphibolous. An oft-quoted example is that of the answer given to Croesus when he consulted the Oracle at Delphi about the advisability of going to war with Persia. It ran “If Croesus went to war with Cyrus, he would destroy a mighty kingdom.”. Croesus was much pleased with this and went to war with Cyrus – a war in which he was quickly defeated. His life was spared and when he complained to the Oracle he was told that the Oracle was right; he had destroyed a mighty empire – his own.
Whether words are accented or not can change the meaning of a sentence. If this occurs in an argument, the fallacy of Accent can be committed. Copi gives the following sentence as an example of meaning variability.
We should not speak ill of our friends.
We can see how the meaning changes when one or more of the italicised words are accented.
Reasoning from the properties of the parts of something to the properties of the whole. A machine composed of many light components may itself be heavy not light.
This is the opposite of composition and is arguing that what is true of the whole is also true of its parts. For instance, if a certain company is important, a Mr. Bloggs who is a member of the company is also important.
Avoidance of Fallacies
There is no easy or certain way of avoiding fallacies. Native intelligence and intuition help but the labels that we have seen can act as sign posts which, if we remember them, should help us recognise fallacious arguments.
I have located a book that would serve well as an introduction and is very inexpensive. It is Logic, A Graphic Guide by Dan Cryan, Sharron Shatil, and Bill Mayblin. It is available from Amazon for £4.54. I will bring my copy in.