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Thread: Inductive, Reductive, and Deductive Reasoning

  1. #1 Inductive, Reductive, and Deductive Reasoning 
    Forum Freshman
    Join Date
    Sep 2012
    I don't study philosophy so go easy on me.

    My understanding is that deductive reasoning goes from several general propositions, to a specific statement. The specific statement will always be true providing the original propositions are true.

    When something is general, doesn't that mean it "usually" applies? For example:

    Generally, women are shorter in height than men.
    Jake is a man.
    Alice is a women.
    Jake is taller than Alice.

    All the propositions are true, but the conclusion to this could be wrong. So how can it be deductive?

    Yet it cannot be inductive because "women are shorter than men", is general in nature.

    If we changed it to this:

    Exactly 90% of the worlds men are taller than Alice (a specific statement)
    Alice is the tallest women at place of work "X" (Specific statement)
    Alex is a women. (a specific statement)
    Alex works at "X" (a specific statement)
    At least 90% of men in the world are taller than Alex (this has to be true (provided the supporting statements are true) - yet it is not a deductive argument because it is based on specific statements).

    How does all this work?

    Finally, I have googled "reductive logic". The results are completely unhelpful. I have also tried to find an explanation of reductive logic in textbooks that I own (I only have science texts), but cannot find an explanation.

    Could someone explain in simple terms what reductive logic is?


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  3. #2  
    New Member
    Join Date
    Apr 2013
    Wow, not many answers.
    So... in case you are still wondering, this is my understanding. Just because something uses deductive reasoning does not necessarily mean the conclusions are correct; the conclusions must be true only if the original premise is also true.
    As for your first example:
    IF "Generally, women are shorter in height than men" THEN Jake (a man) is taller than Alice (a woman). Rewriting this in the form of a deductive argument reveals the weakness in your logic. This is fallacious reasoning and would be considered a fallacy of sweeping generalization since you attempt to make too specific a conclusion based on a rule without considering its know exceptions.
    A more accurate statement would be that the mean height of men is greater than the mean height of woman and a more accurate way of measuring the validity of this statement would be to obtain the heights of men and women from a random sampling of a larger population. Consider perhaps the following statement "Generally, women are shorter in height than men" THEREFORE the women of (insert your favorite city here) will be shorter in height then the men. Note the statement does not say that every man is taller than every woman so measuring the height of one man and one woman is irrelevant to the original statement. Also note that since deductive reasoning relies on the validity of the original general statement, law or truth, if this is inaccurate or inaccurately expressed it can lead to a false conclusion. This does not mean that the reasoning is not deductive, it would make the argument unsound but in invalid. For example, suppose you said "All men are taller than 6 feet. Jake is 5' 10". Therefore Jake is not a man." This is deductive reasoning, and it is a valid argument but it is not sound because the original premise, that all men are taller than 6 feet, is false.
    Your second example is deductive.
    IF (A)"Exactly 90% of the worlds men are taller than Alice" AND (B)Alice is taller than Alex THEN (C)"At least 90% of men in the world are taller than Alex" A is your first premise, B is your second premise. Provided both of these are true then (C) your conclusion should also be true.

    Inductive reasoning: an example would be to say "we at research facility x have decided to record everyone's height. We are wondering if is there a relationship between sex and height. Based upon measuring 100 adults we have found that in general women at facility x are shorter then men. Therefore we conclude that it is probable that in general women are shorter then men everywhere. The conclusion is based upon observation and limited by the observations you can make so it is what is most likely (or most probably) true. From this truth you could then form deductive arguments or hypothesis that could be the basis of experimentation.

    Reductive reasoning: it is an attempt to assign a simple cause to a complex system. An example would be "Jake spent 6 hours working in front of a microscope yesterday therefore Jake is a scientist"

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