When statements are made about a class, sometimes they are about all of the members of it, sometimes about some of them, and at other times it is not clear which is referred to. The fallacy of concealed quantification occurs when ambiguity of expression permits a misunderstanding of the quantity which is spoken of.
Garage mechanics are crooks.
(What, all of them? It does not say, but there is a big difference. If it refers to all of them, then to talk to one is to talk to a crook. Although many motorists may have their convictions, few of the garage mechanics do.)
Very often the quantification is concealed because it sounds rather lame to make bold statements about some of a class. ‘All’ is much better, but probably untrue. Rather than be limited by such a technicality, a speaker will often leave out the quantity in the hope that ‘all’ will be understood. Someone might commiserate with a distraught parent by telling them: ‘Teenagers are troublesome.’ This can be accepted as ‘some are,’ or even ‘many tend to be so’, but it could also be taken to mean that one has only to find a teenager to locate a troublesome person. This may not have been intended, however plausible it sounds. The fallacy comes with the ambiguity. The statement can be accepted with one meaning, yet intended with another. Of course, very different conclusions can be drawn from the two meanings.
It is well known that members of the Campaign for Nuclear Disarmament are communists.
(It is indeed, but not all of them, as seems to be implied. Even if some are communists, there is still room for others motivated by sincerity or stupidity.)
The fallacy is widely used to condemn whole groups on the basis of some of their members.
Subversives teach at the Open University.
(This could mean that some do, but is unlikely to mean that all subversives are so employed. It could even be taken as telling us that only subversives teach there. The quality of the average BA would vary enormously, depending on which were true, as indeed might the course content.)
Concealed quantification can also be a prelude to tarring an individual with the characteristics of the group to which he belongs by hiding the fact that they apply only to some of that group.
Have you ever noticed that bishops are fat? I suppose now that Johnson has been raised to a bishopric he’ll expand a bit himself.
(Weight and see.)
You should use concealed quantification to make a weak case look stronger than it is. If you are trying to sow doubts about a person, you can use their membership of some group to cast general aspersions about them. Make reasonable-sounding statements which are true of some, and allow your audience to supply the ‘all’ or the ‘only’ which are needed to brand him as well.
I don’t think we should hire Thomson. I see he’s a keen fisherman. Idlers take up fishing, so / think it’s a very bad sign.
(The audience take the bait, make it ‘only idlers’, and Thomson is already hooked.)
The above article is from the book How To Win Every Argument by Madsen Pirie. The article is only for educational and informative purposes to explain and understand formal logic and logical fallacies. It is a great book, definitely worth a read!