Past perfect without past simple before

Question

From this answer by Ronald Sole:

[...] To which the patient might reply: I have not eaten anything since yesterday.

That's to say that the last time the patient took food was prior to midnight. It could have been at any point up until midnight, and might have referred to several meals during the course of the previous day.

So your statement means that the person concerned had eaten the previous day, possibly several times, but has not consumed any food since then.

Why the past perfect here, is it because the action was completed to emphasize the completion, or can we add he had eaten the previous day several times before he went to hospital, and would the past simple be possible in that case?

Answer 1

It would appear that the speaker (or author) of this remark:

So your statement means that the person concerned had eaten the previous day, possibly several times, but has not consumed any food since then.

is referring to a statement of yours issued at some time in the past or relating to events that took place at some time in the past. How do we determine this?

The time phrase the previous day never means yesterday. "The previous day" always refers to a day farther in the past than yesterday.

To judge from the speaker's use of the phrase the previous day, your statement cannot have been issued today, and it cannot be about events that took place today. However, that logical conclusion conflicts with the present perfect, "but has not consumed any food since then", which treats your statement as if it were one made just a moment earlier.

The presence of the previous day explains the past perfect had eaten -- the consumption of food was an action that took place in a past time which is earlier than your statement, or earlier than the events it mentions. The time of your statement or the events it mentions is the reference time in relation to which the eating is being situated in time.

My guess is that someone doesn't understand the meaning of the previous day, either that, or is misusing the present perfect. If the speaker/author of the remark quoted above understands the implications of the previous day, the remark would have said ... and had not consumed any food since then.