Informal logic: decomposing arguments

by / 0 Comments / 226 View / August 3, 2015

There are several components of an argument. These can be useful if you want to evaluate the validity of a claim.

  1. Assumption: an unstated fact or principle that must be true in order for the conclusion to be valid.
  2. Premise: a stated fact or principle that must be true in order for the conclusion to be valid (always present).
  3. Counterpremise: a stated fact or principle that seems to contradict the conclusion.
  4. Intermediate conclusion: a claim, reasoned from premises and assumptions, that becomes an additional premise.
  5. Background information: all other facts presented that are not premises.
  6. Final (main) conclusion: a claim, reasoned from premises and assumptions, that conveys the arguer’s position or purpose.

The only piece that is required in every argument is the premise; the simplest argument is Premise-Premise. It is not required to have a conclusion. Consider this simple example:

The only car Jacob owns is a blue Dodge Challenger. The car parked in his spot is a red Ford Mustang.

This argument is Premise-Premise. It implies a conclusion (the red Ford Mustang parked in Jacob’s spot does not belong to Jacob) that the listener should infer (in this case, the implied conclusion must be 100% true given the premises).

More interesting informal arguments contain many assumptions. An assumption is simply a premise that is not stated; if the assumption were stated, it would be a premise. If you find yourself disagreeing with someone else’s claim, it may be helpful to understand what is being assumed and why that may not be a valid assumption.

This graphic is one instance of the now-common advice on the best time to drink caffeine. To quote the core of the argument:

(1) Production of cortisol peaks between 8am – 9am, meaning your body is “naturally caffeinating” itself (albeit without caffeine) during these hours of the day.


(2) If you drink coffee at the same time that your cortisol levels are peaking, the effects of caffeine will be greatly diminished since you’re already experiencing a natural jolt.


(3) By consuming caffeine when it is not needed, your body will build a faster tolerance to it, and the buzz you get from it will greatly diminish.


(4) So, if you find yourself upping your daily caffeine dosage to get the boost your want, instead try drinking your coffee AFTER your cortisol levels have dropped, which happens a few times a day.

The first three lines are premises and the final line is the conclusion (note the key word “so” that usually signals a conclusion). Everything before the core is background information. Notice that there are several assumptions that must be true for the conclusion to be valid, and if the assumptions were not true the conclusion would be undermined or false. We can list a few assumptions:

  • “Diminished effects” are no more desirable than “no effects.”
  • The listener has no interest in upping caffeine dosage (or that doing so would be wrong).
  • The consequences, in any, of shifting time of caffeine intact are less severe than those of caffeine competing with cortisol levels are.

Think about how the conclusion might hold if any of these were not true. For instance, we can accept the scientific fact (premise) that caffeine has a reduced effect early in the morning, but a reduced effect can still be better than none. This is a common assumption, and often an unreasonable one (a marginal benefit is still a benefit). The author also goes from the premise that you will build a tolerance faster (which is true) by drinking coffee when you wake up to the conclusion, “…if you find yourself upping your daily caffeine dosage to get the boost your want, instead…” without ever asking whether drinking more coffee is a bad thing. Perhaps you are able and willing to have two drinks a day without major side-effects. Finally, the author assumes either that there are no consequences to skipping the first cup of coffee or that doing so would be not as bad as building a tolerance. For some of us, missing the early morning caffeine rush would be more detrimental than the increased quickness of tolerance building would be. It is not reasonable to trade one small benefit for a larger cost.

Understanding the structure of an argument can make it easier to understand and evaluate.


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