Question #1060

Combined premises?

Started by Brett-Lindsay · started 2020-07-12 12:12 · last activity 2020-08-02 13:52 · 4 replies

Similar to some of the previous questions, I've combined premises which share the same necessary conditions. I'm just wondering if it's valid or not. If it is, is it valid for both sufficient and necessary? And and or combos? We get two premises from the stimulus: The trees always blossom in May if April rainfall exceeds 5 centimeters. If April rainfall exceeds 5 centimeters, then the reservoirs are always full on May 1. AR>5 --> TBM AR>5 --> RFM1 Can we combine them? AR>5 --> TBM & RFM1 not TBM or not RFM1 --> not AR>5 The reservoirs were not full this May 1 and thus the trees will not blossom this May. not RFM1 --> not TBM I notice that it's taking one of the combined conditions to conclude the existence of the other, which is invalid. The same reasoning holds for answer A.

Replies

  1. shunhe · 2020-07-13 16:32

    Hey @Brett-Lindsay, it is totally fine to combine conditionals like that in that way. A-->B and A-->C can be made into A-->B&C, which can then be made a contrapositive in the way you did it. Good job!

  2. Brett-Lindsay · 2020-07-15 14:09

    Got it. Thanks @shunhe

  3. shunhe · 2020-07-15 17:05

    Yup, glad to help!

  4. erica-scott · 2020-08-02 13:52

    But wouldn't the rainfall be a necessary condition for the trees to blossom? The trees will not blossom without the 5cm of rainfall? Also - if there is two sufficient terminology like we see here (always and if), which one do you choose?

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