We here take the language in its natural order, and obtain a definite and clearly understood meaning.
Another context will show a different relation. The teacher replies as follows:
14-3. The class is composed of one boy and five girls. The boy, who is at home, is my best pupil.
Because of the context, “the boy” needs no identification, no restrictive words to explain who is meant. The sentence could be written thus:
14-4. The class is composed of one boy and five girls. The boy (he is at home) is my best pupil.
In the above sentence the group of words in parentheses explains; but it is not restrictive. It tells something about the boy; but it does not tell what boy, for this information is given in what precedes, which says there is only one boy. In No. 14-3 this group of words is slightly changed, and is given grammatical connection by its form, and thus it becomes only slightly parenthetical.
In Nos. 14 and 14-2 the meaning is not complete without the restrictive words. In Nos. 14-1, 14-3, and 14-4 these words are not essential to identify the boy, being added simply by way of explanation, hence they are called explanatory.
In the consideration of the terms explanatory and restrictive, much confusion arises from the fact that a restrictive group may also be an explanatory group. A purely explanatory group, which requires commas to set it off, is never a restrictive group. This confusion can be entirely avoided by calling the groups restrictive and non-restrictive. The latter group is set off by commas because it conveys a different meaning from that of a restrictive group, and also because it is “slightly parenthetical,” that is, parenthetical in nature, but with grammatical connection.
Not a few writers use the marks of parenthesis or dashes, instead of commas, to set off a non-restrictive (explanatory) group; but, as their writings reveal no differentiation in the uses of these three marks, their system of punctuation is a wholly hit-or-miss one.