50. When there is no break in sense no comma should be used, unless necessary for clearness of expression.
51. Scarcely can a sentence be perused with satisfaction or interest, unless pointed with some degree of accuracy.
No. 50, like No. 49-1, is practically completed at the comma, what follows in each being added as an additional thought. In No. 51 the language up to the comma is almost meaningless, or, at least, makes an untrue statement. What follows the comma _restricts_ the assertion to a definite and true statement, just as what follows the comma in No. 49 _restricts_ the meaning of the assertion made in the language preceding it. Because of this relation between the parts no comma is used, and for the reasons already discussed.
Sentences 50 and 51 are not unlike Sentences 13 and 13-1; and therefore the same reasoning determines their punctuation.
Mr. Wilson’s use of a comma before “unless” in No. 51 is wrong, and is contrary to one of his own rules.
Such mistakes can be found, probably, in the text-book of every writer on punctuation. They are generally mere oversights, and should not be construed as evidence of the writer’s lack of knowledge. It is the system of a writer which determines the value or lack of value of his work.
The punctuation between clauses connected by _when_, _where_, and like connectives, presents difficulties only when an attempt is made to rob such connectives of their apparent meanings, respectively, of time and place, as is done by some writers, and perhaps correctly in rare cases.
In each of our next three illustrative sentences the thought of time is equally manifest; and therefore there is no more need of a comma in one than in the other:
52. You may fire _when_ you are ready, Gridley.
It is true that “when” may lose, at least in a measure, its sense of time, and then indicate a somewhat different relation between the clauses it connects. Mr. Wilson gives the following sentence to illustrate this point:
53. Refrain not to speak, when by speaking you may be useful to others.
Here “when” may not refer to time, but may be equivalent to _if_, thus introducing a condition under which to speak; or it may be equivalent to _because_, thus giving a reason. Such meaning would make a sentence very much like No. 49-1.