The absence of a comma after “imagination” would give notice to the reader that what has been said about “imagination” is to be said about something else in the _and_ relation to “imagination.” The writer, wishing to qualify the added statement, does so before the statement is made, thus throwing matter (one word in this case) between what has preceded and what is to be grouped with “imagination,” as shown by the absence of a mark before “and.” This makes the qualifying word a modified parenthesis. Such treatment of the word, indicated by marks, gives a shade of meaning difficult to express in language. The difference is, perhaps, in the emphasis gained by the punctuation.
We should write the sentence in the following way:
59-1. It is here that composition is of service to the imagination and, incidentally, to culture; and I should speak more largely....
Our next sentence, which is taken from a well-known literary paper, is punctuated so badly that we wonder how it could pass an experienced proof-reader:
60. Providence made him a waif on London streets and later, a waif on the ocean, she taught him the feeling of a rope’s end on a naked back.
When the reader reaches “and” in this sentence he needs to be informed by a mark of punctuation that what immediately follows the conjunction looks forward, not backward, for its connection. Such notice is always imperative when the words immediately following the conjunction may readily be attached by the reader to what precedes, but belong to what follows. In this sentence “a waif on the ocean” readily becomes the object of “made”; and even a very careful reader might so connect it, not discovering his mistake until he reached “she taught him.” “Later” apparently looks backward to “made”; but its connection is forward.
Properly punctuated the sentence reads as follows:
60-1. Providence made him a waif on London streets; and, later, a waif on the ocean, she taught him the feeling of a rope’s end on a naked back.
“Later” takes a comma before it because it is out of its natural order and also because it is placed in a position where it obstructs the smoothness of the language. The position of both “later” and “a waif on the ocean” gives force and beauty to the language; but they entangle, to a certain extent, the principal words of the sentence, thus requiring marks of punctuation to point out the proper relation between such words, as in Sentence 4-2.