Deductive reasoning is reasoning from the general to the particular . In law, deductive reasoning means reasoning based on a general rule of law to determine the appropriate outcome in a specific case: Judges use deductive reasoning to come to a legal conclusion based on a general rule from a previous case The law's reliance on the doctrine of precedent is an example itself of deductive reasoning.
Note: In law, there there is no pure formal logic, logic, as in maths or empirical scientific reasoning, where there is one right answer. In law the rules of logic are applied to try to reach the correct answer.
STANDARD-FORM CATEGORICAL SYLLOGISMS
SYLLOGISM- is deductive argument in which a conclusion is inferred from two premises. Categorical Syllogism- is a deductive deductive argument consisting of three categorical categorical propositions that together contain exactly three terms, each of which occurs in exactly two of t he constituent propositions. Major term- term that occurs as the predicate of the conclusion. Minor term- term that occurs as the subject term of the conclusion. Middle term- term which does not occur in the conclusion, appearing instead in both premises. e.g All P is M. Some S is M. Therefore, Some S is P.
All celebrities are cute. Some law students are cute. therefore, some law students are celebrities.
Major term- celebrities Minor term- law students Middle term- cute
SYLLOGISTIC RULES AND FALLACIES Rule #1. A valid standard-form categorical categorical syllogism must contain contain exactly three terms, terms, each of which is used in the same sense throughout the argument. Explanation: the conclusion of a ca tegorical syllogism asserts that a certain relation holds between two terms . It is clear that the conclusion is justified only if the premises assert the relationship of each of the conclusion’s terms to the third term. term. Were these not asserted by the premises, no connection between two-terms of the conclusion would be established, and the conclusion would not be implied. All categorical syllogism that contains more than three terms is invalid , and is said to commit the fallacy of fo ur terms (quaternion terminorum) Example: Power tends to corrupt Knowledge is power. Therefore, knowledge tends to corrupt.
The middle term “power” is used in different senses in the two premises. In the first premise, the term power means “the possession of control or command over people”, whereas the term “power” in the second premise means “the ability to control things.”
Rules #2: in a valid standard-form categorical syllogism, the middle term must be distributed in at least one premise. If the middle term twice universal, then its extension and supposition in both premises are exactly the same of this rue is called Fallacy of Undistributed Middle term. EXAMPLE: All law students are thinkers Some thinkers are criminals Therefore, some criminals are law students. In this case, the middle term thinker is twice particular. It cannot, therefore, be used to connect law students and criminal- both of them could be separate and unconnected divisions of the class of thinker.
Rule# 3: in a valid standard-form categorical syllogism, if either ter m is distributed in the conclusion, then it must be distributed in the premises. A valid argument is one whose premises logically imply or entail its conclusion. The conclusion of a valid argument cannot go beyond or assert more than is implicitly contained in the premises. A violation of this rule is called the Fallacy of illicit major term. Example: All lawyers are intelligent. No law students are lawyers Therefore, no law students are intelligent.
Rule# 4: No standard-form categorical syllogism having two negative premises is valid. Any negative proposition denies class inclusion, asserting that all or some of one class is excluded from the whose of the other. From two negative premises, there can be no relationship that is established between two terms, and therefore no conclusion can be inferred. Example: No lawyer is a liar. No liar is upright person Therefore, no upright person is a lawyer.
Rule# 5: If either premise of a valid standard-form categorical syllogism is negative, the conclusion must be negative. An affirmative conclusion logically follows only from two affirmative premises. Hence if either premise is negative, the conclusion cannot be affirmative but must be negative also. Any syllogism that breaks rule 5 may be said to commit the fallacy of drawing an affirmative conclusion from a negative premise.
Example: No women are bitter Some sweets are women Therefore, some sweets are bitter
Rule# 6: no valid standard-form categorical syllogism with a particular c onclusion can have two universal premises. To break this rule is to go from premises having no existential import to a conclusion that does. Example: All males of 1-D Class are handsome No intelligent are handsome Therefore some intelligent are not males of 1-D class.
