Have you ever used, heard, or read these cumbersome constructions: “I had had that same experience but then something else happened” or “She said that that car nearly hit her”? My experience suggests that they are being used more frequently but they need not be. The use of “had had” is an attempt to say that something happened in the past but is happening no longer. There are a couple of ways to avoid this clunky expression. If it is not essential to communicate that the episode is not ongoing then use had only once. If it is essential to communicate that the experience was completed in the past then substitute “once” for the first “had” as in “I once had that same experience” or “I have had that experience.” You might use an adverb: “I formerly had that experience.” That’s a little archaic but it might be better than “had had.”
“That that” can be avoided by finding a substitute for the first “that” or the second. This construction usually occurs when one is paraphrasing or summarizing. “I find that that construction is clunky.” The paraphrastic “that” is followed by a demonstrative “that.” It is grammatical but it is also ugly and sometimes disconcerting to the reader. Sometimes the paraphrastic “that” can be omitted with no loss of clarity. “I find that construction to be clunky.” In some cases one can simply omit the demonstrative “that.” The demonstrative can sometimes be replaced with “such as.” American English has a strong impulse to pile up words for emphasis. The construction “that that” is one instance of this phenomenon. Fewer words can be an elegant solution to the problem.
Ps. A correspondent pointed out that Lincoln used “that that” in the Gettysburg Address. Responses: 1. Sometimes it us unavoidable. 2. Most of what is written isn’t the Gettysburg Address.