No comma is required after “holds” in No. 39 because there is no grouping of words in the sentence that requires to be made in order to show a relation different from the relation that exists in the simplest form of expression, such, for instance, as the relation of adjective to noun, noun to verb, verb to object, etc.
In Sentence 40 “that” does not grow out of or coalesce with “is” as “that” grows out of and coalesces with “holds” in No. 39. The reader almost invariably pauses after “is” in such relations, as if to group into a whole what follows, such whole constituting the predicate of the sentence. The comma serves to show a grouping that is at once natural and helpful in reading, whether aloud or silently. This relation, with the need of the grouping, may be shown somewhat more clearly in a sentence where the use of the comma is quite unquestioned by good writers:
41. The benefit of a right good book depends upon this, that its virtues just soak into the mind, and there become a living, generative force.
Let us note that the relation here marked by a comma is quite suggestive of two similar relations which we indicated, respectively, by a colon (Sentence 26-3) and by a comma and dash (Sentence 34). It is plain that the relation in each of the three sentences (Nos. 26-3, 34, 41) is that of apposition; but it takes a different form in each, and so we punctuate the three sentences differently, each sentence falling into a different class.
While the above sentences present no difficulty in their punctuation, the punctuation of other sentences quite like them seems to be somewhat puzzling, yet it is based upon reason.
In court decisions the finding or findings generally appear in a separate paragraph or paragraphs, following a review of the case. The punctuation here is not entirely uniform; but, although it seems inconsistent with that of No. 39, it is easily explained:
If the decision covers two or more points, it may take this form:
2. That the lower court did not err in its instructions to the jury.
If there is a reason for the use of a comma after “held” in No. 42, the same reason seems to require a comma after “held” in No. 42-1, the dash being used for another purpose, to be considered later. A comma is not used in No. 42-1, because its omission is the _conventional_ usage.