Question of Validity in syllogisms of deductive argument

What is validity in deductive arguments?

A deductive argument is said to be valid if and only if it takes a form that makes it impossible for the premises to be true and the conclusion nevertheless to be false.

What is an example of a valid deductive argument?

Premise 1: All dogs are mammals. Premise 2: All collies are mammals. Conclusion: All collies are dogs. To summarize, a valid deductive argument is one where it would be impossible for the conclusion to be false given that the premises were true.

What is the validity and truth of deductive argument?

Below are five different definitions of the same concept. It is common to drop the word deductive from the term deductively valid: An argument is valid if the premises can’t all be true without the conclusion also being true. An argument is valid if the truth of all its premises forces the conclusion to be true.

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How do you determine the validity of a syllogism?


  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.

What should you ask yourself to informally test the validity of an argument?

To apply the informal test of validity ask yourself whether you can imagine a world in which all the premises are true and yet the conclusion is false. If you can imagine such a world, then the argument is invalid. If you cannot imagine such a world, then the argument is valid.

How do you determine the validity of an argument using truth tables?

  1. Symbolize each premise and the conclusion.
  2. Make a truth table that has a column for each premise and a column for the conclusion.
  3. If the truth table has a row where the conclusion column is FALSE while every premise column is TRUE, then the argument is INVALID. Otherwise, the argument is VALID.
  4. 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”.

    What is deductive validity?

    An argument is deductively valid if, and only if, it’s not possible for it to be the case that both, 1) all of its premises are true and 2) it’s conclusion is false, as it were, at the same time. This will be our official definition of deductive validity.

    What is an example of a valid argument?

    A valid argument is an argument in which the conclusion must be true whenever the hypotheses are true. In the case of a valid argument we say the conclusion follows from the hypothesis. For example, consider the following argument: “If it is snowing, then it is cold. It is snowing.

    What are the six rules for validity for a syllogism?

    There are six rules for standard-form categorical syllogisms:

    • The middle term must be distributed in at least one premise.
    • If a term is distributed in the conclusion, then it must be distributed in a premise.
    • A categorical syllogism cannot have two negative premises.

    What is validity in syllogism?

    If a syllogism is valid, it does not have two negative premises. If a syllogism is valid, then it has a negative premise, if and only if it has a negative conclusion. If a syllogism is valid, then if its premises are universal, then its conclusion is universal.

    What is an example of valid syllogism?

    Here is an example of a valid categorical syllogism: Major premise: All mammals are warm-blooded. Minor premise: All black dogs are mammals. Conclusion: Therefore, all black dogs are warm-blooded.

    How do you solve a syllogism question?

    Tips to solve the questions related to Syllogism:

    1. Read the question thoroughly.
    2. Start drawing the Venn diagram.
    3. Follow the sequence of the question while drawing.
    4. Analyse the conclusion from the Venn diagram.
    5. Check for other alternative solutions at the end.

    How would you know that the argument is under syllogism?

    A syllogism is valid (or logical) when its conclusion follows from its premises. A syllogism is true when it makes accurate claims – that is, when the information it contains is consistent with the facts. To be sound, a syllogism must be both valid and true.

    How do you test a 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.

    Can a valid syllogism have false premises?

    A valid argument can have false premises; and it can have a false conclusion. But if a valid argument has all true premises, then it must have a true conclusion.

    When you test syllogism validity with a Venn diagram What do you do to the conclusion?

    Venn diagrams for syllogisms are made similarly to Venn diagrams for propositions.

    1. make the usual two circles. …
    2. Add a third overlapping circle on top. …
    3. Enter the information from the premises into the diagram.
    4. Then read it and see whether the conclusion can be read back out of it.

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