The one-size-fits-all philosophy is an extrapolation of both reasoning systems.

One-size-fits-all thinking assumes as a premise that "if it works for me, its right for you" (or right for anyone else, for that matter—specific to general; that is, Inductive Reasoning). One-size-fits-all thought assumes as another premise that "if it's good for everyone else, it must be good for me" (general to specific; i.e., Deductive Reasoning).To better illustrate this point, let's take vitamin A as an example, from a one sizer's point of view. Numerous research studies have demonstrated the need by all humans for vitamin A. So, the deductive inference is that I as an individual must need vitamin A. Because of this, I'll take my dose as determined by the government, according to the recommended daily allowance or RDA.

Now, because I'm taking the RDA for vitamin A, you should take it as well (as should everyone), because if it's good for me it is good for you. This is an inductive inference. Okay, I'll buy that! This logic has you coming and going as regards Vitamin A, from both an inductive and deductive standpoint that meets, somewhat, in the middle.

What happens when you add to this logical formulation that no two people are the same and therefore have many differing needs? uh-oh— now we can't be sure if one person needs the same amount or type of vitamin A or not, because now we see how false is the assumption that we humans are simply one class of generic bodies, cast from exactly the same mold.

in fact, when it comes to RDA's for vitamin A and all other vitamins and minerals, the Food and Nutrition Board qualifies its RDA data by stating "RDA's should not be confused with requirements for a specific individual. They are not guidelines for formulating diets nor assessing the nutritional status of individuals." Given this information—in order to be logical—we're going to have to go on a case-by-case basis when it comes to nutrition and deductively reason specifically for each individual. Maybe along the way we can find subclasses of humans with similar categorizable physiological traits, where more logical assumptions can be made specific to that particular category of humans. Then perhaps we can make some "partially" accurate deductive and inductive inferences for that human subclass only.

Purely on the "gut" level, one-size-fits-all thinking doesn't make logical sense, given the scientific premise that we are each biochemically unique and therefore have different nutritional needs. Yes, all humans need vitamin A, but that's really all we can safely assume. One-size-fits-all does not give you any qualitative parameters, because it falsely deals with humans as one class of physiological beings. it presumes that we're all made from the same mold, when in fact the quality (as well as quantity) of our needs is directly specific to the individual. Viva la difference! One-size-fits-all is not logical! It is therefore an invalid philosophy.