## Rules of Validity

- Negative Premises and Conclusions -4. If Either Premise of a Valid Syllogism Is Negative, the Conclusion Must Be Negative; if the Conclusion Is Negative, One Premise Must Be Negative

If a premise is negative, it tells us that one class (either

SorP, depending on which premise it is) is excluded from another class (M). From this information, we might be able to infer that S is excluded fromP--if the other rules are satisfied. However, we could never infer thatSis included inP.Conversely, if the conclusion is negative, it says that

Sis excluded fromP. The only information that would justify this conclusion is the information thatSis excluded fromM(which is included inP) or thatSis included inM(which is excluded fromP). In either of those cases, we have one negative premise.

Comprehension Questions

1.Is an E proposition affirmative or negative?a)It is affirmative. b)It is negative. 2.Is an I proposition affirmative or negative?a)It is affirmative. b)It is negative. 3.Is an A proposition affirmative or negative?a)It is affirmative. b)It is negative. 4 .Is an O proposition affirmative or negative?a)It is affirmative. b)It is negative. 5.If the major premise is negative, then the conclusiona)must be negative b)can be negative 6.If the conclusion is negative, then one premisea)must be negative b)can be negative 7.If the minor premise is negative, then the conclusiona)must be negative b)can be negative 8.If one premise is an E proposition, then the conclusiona)must be negative b)can be negative 9.If one premise is an O proposition, then the conclusiona)must be negative b)can be negative 10.If one of the premises is an A proposition, must the conclusion be and O or an E proposition?a)yes b)no 11.If one of the premises is an I proposition, must the conclusion be an O or an E proposition?a)yes b)no 12.Does the following syllogism violate the rule that the conclusion must be negative if one of the premises are and that one of the premises must be negative if the conclusion is?

No horned animal is a carnivore

All moose are horned animalsSome moose are not carnivoresa)yes b)no 13.Does the following syllogism violate the rule that the conclusion must be negative if one of the premises are and that one of the premises must be negative if the conclusion is?

No M is P

All M is SSome S are Pa)yes b)no 14.Does the following syllogism violate the rule that the conclusion must be negative if one of the premises are and that one of the premises must be negative if the conclusion is?

All supporters of the nuclear freeze want to preserve peace

No conservatives support nuclear freezeNo conservatives want to preserve peacea)yes b)no

Two Negative Premises | Negative Premises and Conclusions

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