HELP - Flaw Questions: Sufficiency-Necessity confusion

Mihael K.Mihael K. Alum Member
in Logical Reasoning 76 karma

In the flaw section of LR, I have a hard time understanding the common argument flaw of sufficiency-necessity confusion, as JY calls it. I never seem to recognize a flaw argument that is committing the sufficiency-necessity confusion flaw.

Due to this, can anybody show me an example of an argument that is committing this flaw and explain to me how it constitutes a sufficiency-necessity confusion? Thanks.

Comments

  • EveryCookCanGovernEveryCookCanGovern Alum Member
    edited February 2020 401 karma

    If it rains tomorrow, it will be cloudy tomorrow. But I know for certain that it will not rain tomorrow. therefore it will not be cloudy tomorrow.

    Symbolizing this flaw looks like this:

    RT -> CT
    RT(not)
    __
    CT(not)

    The conclusion does not follow from the premises here. But it does follow from the premises if the sufficiency/necessity relationship between RT and CT would be switched:

    CT -> RT
    RT(not)
    __
    CT(not)

    This is logically sound, but that's not the conditional relation that the premises outlined. So the author confuses the necessary condition for the sufficient condition (and the sufficient condition for the necessary condition, which is saying the same thing since they're just switching places).

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