The same ambiguity attends "not … and." "I do not see Thomas and John" is commonly used for "I see neither Thomas nor John;" but it might mean, "I do not see them both—I see only one of them."
*That.*—The different uses of "that" produce much ambiguity, e.g. "I am so much surprised by this statement that I am desirous of resigning, that I scarcely know what reply to make." Here it is impossible to tell, till one has read past "resigning," whether the first "that" depends upon "so" or "statement." Write: "The statement that I am desirous of resigning surprises me so much that I scarcely know &c."
*4 a. Be careful in the use of ambiguous words, e.g. "certain."*
"Certain" is often used for "some," as in "Independently of his earnings, he has a certain property," where the meaning might be "unfailing."
Under this head may be mentioned the double use of words, such as "left" in the same form and sound, but different in meaning. Even where there is no obscurity, the juxtaposition of the same word twice used in two senses is inelegant, e.g. (Bain), "He turned to the left and left the room."
I have known the following slovenly sentence misunderstood: "Our object is that, with the aid of practice, we may sometime arrive at the point where we think eloquence in its most praiseworthy form to lie." "To lie" has been supposed to mean "to deceive."
*5. Be careful how you use "he," "it," "they," "these," &c.* (For "which" see 8.) The ambiguity arising from the use of he applying to different persons is well known.
"He told his friend that if he did not feel better in half an hour he thought he had better return." See (6) for remedy.
Much ambiguity is also caused by excessive use of such phrases as in this way, of this sort, &c.
"God, foreseeing the disorders of human nature, has given us certain passions and affections which arise from, or whose objects are, these disorders. Of this sort are fear, resentment, compassion."