Logical & Critical Thinking

with Professor Logic

Is-Ought Fallacy

The is-ought fallacy is when someone assumes a conclusion based on an ‘ought’ rather than an ‘is’. The major problem is that an ‘ought’ is often derived from an instinct, false premise, or  cultural morality.

Is-Ought Fallacy Structure

Argument: A ought to be B therefore C

Reality: C cannot be logically verified by the ‘ought’ connection of A and B



5 Responses to Is-Ought Fallacy

  1. Guest says:

    Dear Professor Logic,

    This is incorrect.  Go get a decent book on the fallacies.  And stop misleading people.

     a real logic professor

    • Guest 2 says:

      If you are going to criticize someone then you should have a better solution ready to offer. If you are not going to correct them, telling the world they are wrong is pretty much useless.

    • Professor Wag says:

      “stop misleading people”
      Unless you can prove this he/she is misleading, you are making the fallacy of personal attack.

  2. Guest 2 says:

    yeah your explanation of the is ought fallacy is wrong. Its more like 
    Therefore C
    Because of C, D OUGHT to be so and so or it will be immoral.  

    You see, this fourth statement makes no sense. Heres an example:
    It is cloudy outside
    When it is cloudy it rains
    It is most likely going to rain
    Because it will rain, I should take an umbrella.

    Because of the omission of the preposition, “I do not want to get wet” this argument is committing the is ought fallacy.

    Basically, all morality is thought to be removed from absolute logical thought by this fallacy.


    in reality its actually rather simple to solve when you take into account a few things
    Free agency
    The inability of man to NOT act.
    The inherent requisite of consequences coming from actions
    The innate desire of all humans to desire to feel good in the long run over feeling bad.

    With those basic building blocks you can solve the is ought fallacy in my opnion.