Another quite simple form of this grouping, based upon the sense relation, is sometimes overlooked by distinguished writers, and even by authors of text-books on language. The following sentence exhibits both a correct grouping and a correct sense relation:
10. He is in doubt about the best course for him to pursue; but I am sure about the best course for me to pursue.
Here the but relation is between his doubt and my certainty, as if written, He is in doubt; but I am sure.
A similarly formed sentence may convey a meaning that is clearly not the meaning the writer wishes to convey:
10-1. He is in doubt about the best course for him to pursue; but I am sure his doubt will soon disappear.
The but relation in No. 10-1 is not between his doubt and my certainty, as in No. 10. The meaning of No. 10-1 may be expressed thus: He is in doubt; but his doubt will soon disappear. But the assertion made in the latter part of this statement is too strong, and requires a modifier. “Probably” would nearly express the meaning intended to be expressed by the modifier in No. 10-1. If “I am sure” is preferred as the modifier, its relation to the verb (will disappear) must be made unmistakable. It is not so made in No. 10-1, for it appears to be connected by “but” with what precedes it, just as it is connected with what precedes it in No. 10. To disconnect it, a comma precedes it; and one follows it to disconnect it from what follows.
The new relations are shown by the following punctuation:
10-2. He is in doubt about the best course for him to pursue; but, I am sure, his doubt will soon disappear.
Suppose the sentence read as follows, how would it be punctuated?
10-3. He is in doubt about the best course for him to pursue; but I am sure that his doubt will soon disappear.