Formal Fallacy - in Contrast To Informal Fallacy

In Contrast To Informal Fallacy

As modus ponens, the following argument contains no formal fallacies.

  1. If P then Q
  2. P
  3. Therefore Q

If statements 1 and 2 are true, it will absolutely follow that statement 3 is true. However, it may still be the case that statement 1 or 2 is not true. For example:

  1. If a scientist makes a statement about science, it is correct.
  2. Albert Einstein states that all quantum mechanics is deterministic.
  3. Therefore it's true that quantum mechanics is deterministic.

In this case, statement 1 is false. The particular informal fallacy being committed in this assertion is argument from authority. By contrast, an argument with a formal fallacy could still contain all true premises:

  1. If Bill Gates owns Fort Knox, then he is rich.
  2. Bill Gates is rich.
  3. Therefore, Bill Gates owns Fort Knox.

Though, 1 and 2 are true statements, 3 does not follow because the argument commits the formal fallacy of affirming the consequent.

An argument could contain both an informal fallacy and a formal fallacy yet have a correct conclusion, for example, again affirming the consequent:

  1. If a scientist makes a statement about science, it is correct.
  2. It's true that quantum mechanics is deterministic.
  3. Therefore a scientist has made a statement about it.

Read more about this topic:  Formal Fallacy

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