Categorical form & getting the subject right

Mr. Nance,

In the Introductory Logic video Lesson 12, you write this sentence on the white board: “Some days the sun just doesn’t shine.” The first rule to put this sentence into the proper form states: Identify and write the complete subject. You identified “days” as the subject. Essentials taught me to ask, “Who or what does (not) shine?” Doesn’t that mean that “the sun” is the subject? How imperative is it that the subject be identified correctly? 

Great question! If we were to approach this in a purely grammatical way, then “the sun” would be the subject, because that is what is doing the action of shining (or not). Given that subject, it is difficult to translate this statement into categorical form while maintaining the original meaning.  Would it be “Some suns are not day shining suns”? Or would it be “No suns are every day shining suns”? Or what?

A better approach is to translate this statement by starting with the form, then carry across the meaning. It is clearly a particular negative, given the “some” and the “doesn’t.” That means we need to translate it into Some S is not P form. Though grammatically the sun is the subject, logically this statement is talking about different kinds of days, some of them being sunny, and some of them not. A better translation is thus “Some days are not days the sun shines” or simply “Some days are not sunny days.” This carries the same meaning, is easy to understand, and could be readily used in analyzing its relationship with similar statements. 

Think of it this way. Logic is like a foreign language, within which certain special rules must be followed, rules that are different from those of grammatical English. As we translate regular sentences into standard categorical form we must follow these rules:

1) The statement must begin with All, No, Some or Some…Not
2) The verb must be a ” to be” verb:  is, are, was, were, will be
3) Both the subject and predicate must be nouns.

In addition, the original statement and the translation must have the same meaning.

In this case: “Some days the sun just doesn’t shine. “

Some days — answers rule #1 & 3
are not — “to be” verb – rule #2
sunny days — Predicate (also a noun) – rule #3

Thus, “Some days are not sunny days.” If we attempt to make the sun the subject, we cannot easily follow these rules.


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