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As time progressed, we realized that the zero is not a counting number (since you can’t actually count something that’s not there), but is a quantifier nonetheless (it does denote the quantity of nothingness). Hence it is not “natural” but was called a “whole” number.
Negative integers are quantities that are only a different perspective of looking at the natural numbers. For example, if you spend $100 on a small business, and suffer a loss of $150, then you are left with a “deficit of $50” (i.e., if you wish to talk in terms of an actual, physically interpretable, counting number), or from a different perspective, you are left with –50 dollars. Thus you see, if you actually figure out the meaning of –50, you realize that it’s actually a notation for a “deficit of 50”, not “the number –50 per se”. While “50” means “50” in the most elementary interpretation, “–50” does not mean “–50” in the most elementary interpretation. It does not refer to something you can count directly; the negative sign is only a tool to refer to a deficit of a quantity you can count directly.
Therefore, we can’t treat negative numbers as “natural”. They are only a “perspective” of looking at counting numbers differently, not pure counting numbers per se.