Sometime ago, I asked a question about something like example (1a) below.

(1a) Jack, how did you fix the dvd drive in my computer. I replied, "What I did was that I took it out, found a crack in it and put some glue to close the crack."

Gustavo, thanks for correcting my example similar to the one above, and you suggested correcting it, as shown in (1b).

(1b) Jack, how did you fix the dvd drive in my computer. I replied, "What I did was take it out, find a crack in it, and put some glue to close the crack."
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You would use (1b) to explain a process. What if you have something slightly different like (2a) below.

(2a) Your answer to the math problem is wrong. What you did wrong was that first you added these two numbers incorrectly and then you multiplied the sum by the wrong number.

(1a) and (2a) are made up in the same way. To fix it, do I use the suggested solution from (1b), as shown below.

(2b) Your answer to the math problem is wrong. What you did wrong was first add these two numbers incorrectly and then multiply the sum by the wrong number.
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If (1a) is wrong, then (2a) is also wrong. Similarly, if (1b) is right, then (2b) is also right.

Please clarify this further. Many thanks.

Original Post
ansonman posted:

(1a) Jack, how did you fix the dvd drive in my computer. I replied, "What I did was that I took it out, found a crack in it and put some glue to close the crack."

(1b) Jack, how did you fix the dvd drive in my computer. I replied, "What I did was take it out, find a crack in it, and put some glue to close the crack."
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(2a) Your answer to the math problem is wrong. What you did wrong was that first you added these two numbers incorrectly and then you multiplied the sum by the wrong number.

(2b) Your answer to the math problem is wrong. What you did wrong was first add these two numbers incorrectly and then multiply the sum by the wrong number.
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If (1a) is wrong, then (2a) is also wrong. Similarly, if (1b) is right, then (2b) is also right.

Interesting question, Ansonman. I'm afraid your assumption above:

If (1a) is wrong, then (2a) is also wrong. Similarly, if (1b) is right, then (2b) is also right.

is not correct. The word "wrong" after the verb "do" in sentence (2a) allows for the use of a content clause in the predicate of the pseudocleft sentence. Its absence forces you to use a nonfinite clause in (1b). My impression is that "do wrong" forms a lexical unit, which is not the case if some other word more loosely connected with "do," like "then" or "there," is used, as I'll show below. I've made some changes in your sentences (1a) and (1b) for them to sound more natural, at least to me:

(1a) What I did was that I took it out, found a crack and used some glue to fix it. (objectionable)

(1b) What I did was take it out, check it for cracks and use some glue to fix any. (I don't think that "finding cracks" is something you can propose to do in advance, but I might be wrong and this is outside the scope of your question.)

(2a) What you did wrong was that first you added these two numbers incorrectly and then you multiplied the sum by the wrong number.

(2b) What you did wrong was first add these two numbers incorrectly and then multiply the sum by the wrong number.

The presence of "first" makes me feel that a "to"-infinitive fits better:

(2c) What you did wrong was to first add these two numbers incorrectly and then multiply the sum by the wrong number.

With adverbs like "then" or "there" after "do," or an adverbial mainly of time, I think that a nonfinite will continue to be the best choice:

(3a) What I did then was take it out, check it for cracks and use some glue to fix any.

(3b) What I did there was take it out, check it for cracks and use some glue to fix any.

When the verb in the predicate of the pseudocleft refers to the same subject of the free relative with "do," a "that"-clause will not sound idiomatic. The presence of an adverbial of manner like "wrong" seems to be an exception. It seems to me that adverbials of manner qualify what follows, and the fact that a content clause can thus be qualified explains why finite clauses are accepted with "do wrong."

These are some examples (there are not many) I found on COCA. Notice that with "do wrong" in the subject we can find a full infinitive, a bare infinitive, or a "that"-clause in the predicate.

- What you did wrong was to be born smarter and more talented than Eric.
- What he did wrong was to interrupt and reverse the process before it was complete.
- What he did wrong was build a 25- to 30-year broadcasting career on humor that's racist ...
Well, what he did wrong was, he put on evidence that he knew was mistaken. ("that" can be omitted, mainly in colloquial speech.)

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