Why does Gensler’s Star Test not work on some syllogisms?

The syllogism is valid if and only if every capital letter is starred exactly once and there is exactly one star on the right-hand side. The test has limitations, however. It only applies to categorical syllogisms, and even to those only if we make a modern assumption that “All” does not carry existential import.

What makes a categorical syllogism invalid?

If both of the premises are particular (they talk about particular individuals or “some” members inside or outside a particular class, and so can’t be converted into conditionals), then the syllogism will be invalid.

Are all syllogisms valid?

In other words, any syllogism with two particular premises and a universal conclusion will be invalid. The conclusion we just reached is a generalization about all syllogisms, and it tells us that a certain class of syllogisms cannot be valid.

How do you determine the validity of categorical syllogisms?


  1. The argument must have exactly three terms.
  2. Every term must be used exactly twice.
  3. A term may be used only once in any premise.
  4. The middle term of a syllogism must be used in an unqualified or universal sense.
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How do you do the STAR test in logic?

The star test can be applied by using a three-part procedure: 1) underline the distributed letters, 2) star the distributed (underlined) letters in premises and undistributed (not underlined) letters in conclusion, 3) see how many times every letter is starred and how many starred letters there are on the right hand …

What are the valid categorical syllogisms?

Valid syllogistic forms

In syllogistic logic, there are 256 possible ways to construct categorical syllogisms using the A, E, I, and O statement forms in the square of opposition. Of the 256, only 24 are valid forms. Of the 24 valid forms, 15 are unconditionally valid, and 9 are conditionally valid.

What are the fallacies if the rules of structure of a categorical syllogism are violated?

An argument that violates this rule is said to commit the fallacy of drawing an affirmative conclusion from a negative premise. Fallacy: Drawing an affirmative conclusion from a negative premise, or drawing a negative conclusion from an affirmative premise.

What are the 24 valid syllogisms?

According to the general rules of the syllogism, we are left with eleven moods: AAA, AAI, AEE, AEO, AII, AOO, EAE, EAO, EIO, IAI, OAO. Distributing these 11 moods to the 4 figures according to the special rules, we have the following 24 valid moods: The first figure: AAA, EAE, AII, EIO, (AAI), (EAO).

Is syllogism a fallacy?

A syllogism is an argument that has a major premise, a minor premise and a conclusion, and often appears in the form ‘A is B, C is D, therefore E is F’. This is a specific form of argument with very specific rules that are easy to break. In many ways, syllogistic fallacies are the ‘classic’ form of fallacy.

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What are some of the most common invalid argument forms?

2. Common Invalid Argument Forms: There are two very common INVALID argument forms which look a lot like modus ponens and modus tollens, but are mistaken. Arguments with this form are generally invalid. This form of argument is called “affirming the consequent”.

Why is a syllogism invalid?

A valid syllogism is one in which the conclu- sion must be true when each of the two premises is true; an invalid syllogism is one in which the conclusions must be false when each of the two premises is true; a neither valid nor invalid syllogism is one in which the conclusion either can be true or can be false when …

How do you test syllogism?

To test a syllogism for validity we Venn diagram the premises and inspect the result. If the diagram of the premises excludes the possibility of the conclusion being false, then the syllogism is valid.

What are the 5 rules for syllogism?

Syllogistic Rules

  • The middle term must be distributed at least once. Error is the fallacy of the undistributed middle.
  • If a term is distributed in the CONCLUSION, then it must be distributed in a premise. …
  • Two negative premises are not allowed. …
  • A negative premise requires a negative conclusion; and conversely.

Can there be a syllogism which violates all five rules?

If the syllogism passes the rule, put a check mark under the corresponding number and if it breaks the rule, put an X. If it breaks any rule, then the argument is invalid. It must pass all five rules to be valid.

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What does a fourth term do in a syllogism?

Explanation: When you add in a fourth term to a categorical syllogism that can only have three terms to be logically valid, we get nonsense — or at least an invalid argument. Example #2: All Greek gods are mythical.

What are the techniques for syllogisms?

Rules of Syllogism

  • Rule One: There must be three terms: the major premise, the minor premise and the conclusion — no more, no less.
  • Rule Two: The minor premise must be distributed in at least one other premise.
  • Rule Three: Any terms distributed in the conclusion must be distributed in the relevant premise.

How do you master syllogism?

Syllogism Tricks and Tips

  1. Always pay attention to words like ‘some’, ‘a few’, ‘all’, ‘atleast’, etc. These words form the base to solve the syllogism questions.
  2. The best syllogism trick is to solve questions in the form of Venn diagrams. …
  3. Never assume anything while solving the syllogism questions.

Is syllogism there in CAT?

Syllogism is an influential concept of CAT. It has its role in logical reasoning and verbal ability section as well. There are approximately 3-4 questions based on it. And these many questions can play vital role in upgrading your percentile.