How to diagram "that" in a sentence. For example, "I am persuaded that he is able to do it."
Reed-Kellog would say that "that" is a "function word" simply serving the function of introducing a noun clause. MikeNewYork is right. It does not need to be there. It is like "dass" in German. In a R-K diagram it would go on a "stand" made by a dotted line above the simple predicate "is". (I think) Actually this is quite interesting. I think that "he is able to do it" is an objective complement -- something often forgotten. It would be analogous to "angry" in "I am made angry" ( I am caused to be angry.) or "chairman" in "I am elected (to be) chairman. Compare to "The sun made the tomatoes ripe" Not sure about this. It should make for some discussion.
"I think that he is able to do it" would be very easy. The fact that "I am persuaded" is in the passive voice complicates things. In any case, "that" is not a conjunction but rather a function word, like "if" in "I wonder if it will rain." Although in that case the "if" serves more of a purpose.
I am quite sure that according to Reed-Kellogg, the word "that" is never a conjunction. The word "if" certainly can be.
"That" can be a relative pronoun, a demonstrative adjective, a demonstrative pronoun, or a "function" word, but not a conjunction. True, "funtion word" is not one of that practically sacred number of EIGHT parts of speech, but interjections are suspect in that they are not bound by syntax, and expletives are also a little different.
But, if it comforts, one to think of this "that" in a group with "because, when, before, as," etc., then ok.
It is simply not what Reed-Kellogg would say. And the original request was how to diagram it. This "that" has a very special job to to. It introduces noun clauses and does not need to be there.
I suspected as much. In any case, we wait for the diagram.
Actually, I should not leave it at that. Calling "that" a conjunction is a cop out. "That" is different. Sometimes linguists refer to the decay of the cases or gender, or something like that, referring to the way that languages have tended over time to become more simple. I believe that the same may be true for descriptive grammar. "That" is not like "other" conjunctions. Consider "dass" in German. But, if "that" so used must have a quick title, as a dictionary would tend to give, "conjunction" is not bad.
But... the diagram?