What I did is... Or What I did was..

[Michael E. Galario]

Hi sir,

Good day! =)

Could you please explain what tense should be used when a noun clause is used as a subject of the sentence.

Example:

What I did was a mistake.
What I did is a mistake.

My stand here is either present or past these can be used in such construction.
My understanding here is the past form can be used if the action is regarded as already past. The realization of the act in the noun clause completely happened in the past. The second example conveys the idea that the realization is still true.

Please do shed light on this usage.

Thanks sir Joe. =)

[Joe Carillo]

You’re absolutely correct that either the present tense or past tense can be used for that sentence, but the context will be different for each construction. The past-tense “What I did was a mistake” is appropriate if the statement was made in retrospect by the writer or speaker, with the realization of the mistake having definitely occurred in the past and not right before the moment of speaking or writing about it. On the other hand, the present-tense “What I did is a mistake” is appropriate if the statement is made at present or at the very moment of speaking, with the realization of the mistake having just sunk in; in this case, the sense of “What I did is a mistake” is precisely the same as that of “I made a mistake” as a spur-of-the-moment remark.