I received an interesting email from a visitor asking about the form of “to do” + infinitive, in this case in a past simple sentence. It was a complex sentence, which someone hides what is a rather simple, and useful, grammar construction – that we use a construction like “I did like the film” as an affirmative statement. So let’s look at some examples, the rules, and how the rules might be applied even when it doesn’t seem obvious.

To start, the sentence the question regarded was this rather advanced example (don’t worry if it’s too difficult for now, we’ll come back to it!):

“Although they concluded that there is no definitive answer as to which should come first, they did assert that both conceptual and procedural knowledge is important.”

When we use “to do” + bare infinitive

I did cook dinner.

This construction can be used with any verb, in many contexts, simply to emphasise that something is true, correct or was complete. It is mostly used when the action being confirmed has already been mentioned, or is understood. In the above example, it would make sense in this context:

A: “You said you would cook dinner yesterday.”

B: “I did cook dinner!”

In fact, when we answer questions with short forms such as “I am” and “I did”, we are using the same construction: an affirmative statement that has been simplified.

A: Did you walk the dog?

B: Yes, I did (walk the dog).

So we use “to do”, in various tenses, with an infinitive, to confirm that something happened.

Using “did do” as a contrast

As this construction emphasises an affirmative, we often also use it in contrasting a negative. For example:

I didn’t wash the dishes, but I did clean the sink.

This becomes more complex when you consider that the first clause may express a negative sentiment (for example that something was not complete) without directly presenting a negative statement.

Which brings us back to the original example.

“Although they concluded that there is no definitive answer as to which should come first, they did assert that both conceptual and procedural knowledge is important.”

The first statement isn’t framed clearly as a negative – but it does express a failure to do something (they reached no conclusive answer), in contrast to something that they did successfully (asserted that knowledge is important).

In a simpler form, it might read: