Copi, Irving M. Introduction to Logic, 14th Edition . Routledge.1 INSTRUCTIONS Rewrite each of the following syllogisms in standard form, and name…


2. Some evergreens are objects of worship, because all fir trees are evergreens, and some objects of worship are fir trees.

3. All artificial satellites are important scientific achievements; therefore some important scientific achievements are not U.S. inventions, inasmuch as some artificial satellites are not U.S. inventions.

4. No television stars are certified public accountants, but all certified public accountants are people of good business sense; it follows that no television stars are people of good business sense.

 5. Some conservatives are not advocates of high tariff rates, because all advocates of high tariff rates are Republicans, and some Republicans are not conservatives.

6. All CD players are delicate mechanisms, but no delicate mechanisms are suitable toys for children; consequently, no CD players are suitable toys for children.

7. All juvenile delinquents are maladjusted individuals, and some juvenile delinquents are products of broken homes; hence some maladjusted individuals are products of broken homes.

8. No stubborn individuals who never admit a mistake are good teachers, so, because some well-informed people are stubborn individuals who never admit a mistake, some good teachers are not well-informed people.

9. All proteins are organic compounds, hence all enzymes are proteins, as all enzymes are organic compounds.

10. No sports cars are vehicles intended to be driven at moderate speeds, but all automobiles designed for family use are vehicles intended to be driven at moderate speeds, from which it follows that no sports cars are automobiles designed for family use.


Write out each of the following syllogistic forms, using S and P as the subject and predicate terms of the conclusion, and M as the middle term. (Refer to the chart of the four syllogistic figures, if necessary, on p. 235.) Then test the validity of each syllogistic form using a Venn diagram.

Example Problem


Example Solution

We are told that this syllogism is in the first figure, and therefore the middle term, M, is the subject term of the major premise and the predicate term of the minor premise. (See chart on p. 235.) The conclusion of the syllogism is an E proposition and therefore reads: No S is P. The first (major) premise (which contains the predicate term of the conclusion) is an A proposition, and therefore reads: All M is P. The second (minor) premise (which contains the subject term of the conclusion) is an E proposition and therefore reads: No S is M. This syllogism therefore reads as follows:

All M is P.

No S is M.

Therefore no S is P.

Tested by means of a Venn diagram, as in Figure 6-10, this syllogism is shown to be invalid.

Figure 6-10


2. EIO-2

3. OAO-3

4. AOO-4

5. EIO-4


Put each of the following syllogisms into standard form, name its mood and figure, and test its validity using a Venn diagram:


1.Some reformers are fanatics, so some idealists are fanatics, because all reformers are idealists.

2.Some philosophers are mathematicians; hence some scientists are philosophers, because all scientists are mathematicians.

3.Some mammals are not horses, for no horses are centaurs, and all centaurs are mammals.

4.Some neurotics are not parasites, but all criminals are parasites; it follows that some neurotics are not criminals.

5.All underwater craft are submarines; therefore no submarines are pleasure vessels, because no pleasure vessels are underwater craft.


Identify the rule that is broken by any of the following syllogisms that are invalid, and name the fallacy that is committed:

Example Problem

All chocolate éclairs are fattening foods, because all chocolate éclairs are rich desserts, and some fattening foods are not rich desserts.

Example Solution

In this syllogism the conclusion is affirmative (“all chocolate éclairs are fattening foods”), while one of the premises is negative (“some fattening foods are not rich desserts”). The syllogism therefore is invalid, violating the rule that if either premise is negative the conclusion must also be negative, thereby committing the fallacy of drawing an affirmative conclusion from a negative premise.


2. All inventors are people who see new patterns in familiar things, so all inventors are eccentrics, because all eccentrics are people who see new patterns in familiar things.

3. Some snakes are not dangerous animals, but all snakes are reptiles, therefore some dangerous animals are not reptiles.

4. Some foods that contain iron are toxic substances, for all fish containing mercury are foods that contain iron, and all fish containing mercury are toxic substances.

5. All opponents of basic economic and political changes are outspoken critics of the liberal leaders of Congress, and all right-wing extremists are opponents of basic economic and political changes. It follows that all outspoken critics of the liberal leaders of Congress are right-wing extremists.

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