19. The word, eagle, is derived from the Latin.
19-1. The word eagle is derived from the Latin.
In No. 19 “eagle” is used to explain what word, and might very properly go into the class of words that we have called purely parenthetical. It seems to be more closely allied to the class of appositives, and thus takes a grammatical relation which makes it slightly parenthetical, or explanatory.
In No. 19 “word” is the subject of the sentence; “eagle” shows with what “word” we are dealing. In No. 19-1 “word” is adjectival in meaning, and can no more take a comma than can “good” in “good man.” “Eagle,” as a word, is the subject of the sentence.
19-2. His son John did all the work on the farm.
19-3. His son, John, did all the work on the farm.
In No. 19-2 we are told that one of his sons, named “John,” did the work. In No. 19-3 we are told that his son, not his daughter nor one of his sons, did the work. “John” is simply explanatory, as is “who is at home” in No. 14-3.
In Nos. 19 and 19-3 we have language that expresses a different meaning from that expressed in Nos. 19-1 and 19-2; and therefore we use the commas to show that the apparent meaning of the two former sentences is not the real meaning of the two latter.
VOCATIVES
Likewise the so-called vocatives, or words of address, come, though somewhat indirectly, under this same classification and reasoning:
19B. Ring out, wild bells.
If expressed in full, the sentence would read as follows: