I have never had this problem before. But after seeing some questions posted on ELU, I started to doubt. I have been through links1, pages of grammar books2, a lot of questions3 posted here and ELU. I now still can't seem to understand how the past perfect is exactly used. The references sometimes even contradict each other.
What I had understood so far was
The past perfect is not necessary if we are not 'going back' to the earlier past, and simply moving from one event to another.
but I then saw a lot of other 'rules' including
If the sequence is clear, the past perfect is not needed.
which is slightly different, less 'narrow' and can be applied in more situations than the first ruleA, and
The past perfect is optional only when talking about an action at a specific time.
This is confusing. Can anyone here clarify things out please?
A For example, for
Doing the survey [completed] -> Showing the result
We showed the result of the survey we did.
If the second rule is applied, the sentence above is fine (the sequence is clear), but not if the first rule since we are not moving from any event to the next and possibly even going back.
1 English Pages and English Grammar Secrets
2 Practical English Usage (2005) by Michael Swan, Collins Cobuild Student's Grammar (1991). Upper-Intermediate Cutting Edge.
3 including Is it possible to be grammatically correct without using past perfect?, When is using the past perfect tense not necessary?, Past vs Past Perfect, Past Perfect sentences with “before” etc.
Best Answer
The truth is that there are many situations and sentences which allow for either the past perfect tense or the past simple tense, with very little change to the sentence. The key difference between the past perfect and past simple tenses is the explicit order of two (or more) events in the past. There are of course many nuances in usage that make this a fairly complex topic, which I can only partly cover here. First, here is a brief overview of some of the relevant usages and rules of past simple and past perfect:
Past Simple
The third point is where the past simple tense overlaps with the past perfect tense, and is what I will be focusing on.
Simple tenses are often represented as a single dot on a timeline, such as the one below. In the case of past simple, this represents that the event is completed entirely in the past. If past simple is used to list multiple events, then we represent it with multiple unconnected dots in the past, arranged in chronological order.
Past Perfect
Perfect tenses are often represented by two dots with a connecting "bridge" on the timeline. This represents both the order (past perfect clause = left dot; past simple clause = right dot) and linking of the two events.
Note: I find that timelines such as this often help my students understand tense usage better. This particular timeline is one I use often and is from this site.
The past perfect is not necessary if we are not 'going back' to the earlier past, and simply moving from one event to another.This is correct. Past simple can be used to list multiple events in the past, but they should always be in order of occurrence, from longest ago to most recent (or have some other way of explicitly stating the order of events).
If we use the past perfect tense instead, then we have more flexibility in the sentence structure while still being grammatically correct.
or
You can see that when using the past perfect tense we can list events in whichever order we prefer, rather than being restricted to chronological order.
If the sequence is clear, the past perfect is not needed.Again, this is correct. However, there are nuances here. For the sequence to be "clear" you must either list events in chronological order as I mentioned before, or explicitly state the order or time in the sentence. This is often ignored by native speakers because the order of events can usually be inferred from the sentence without it being explicitly stated. In fact your example sentence shows this phenomena. I will again denote longest ago and most recent.
We can in this case correctly infer that the survey was completed before the results were shown, it is simple logic. However, if you wish to be more clear (and grammatically correct) then it is better to write it in the past perfect tense.
I recommend my students to always use explicit ordering of events for the sake of clarity, so that the reader/listener does not need to use logic to deduce the order. Most prefer to do this by using the past perfect tense, or chronological order of events in the past simple tense.
The past perfect is optional [i.e. may be replaced by past simple] only when talking about an action at a specific time.This "rule" is a combination of the usage rules for past simple and past perfect. As I mentioned before, one of the rules of past simple is that it must include a time, which can be either implied or specified. However, when the past simple is used to replace the past perfect, more information (i.e. a specific time) is needed to provide the same information to the reader/listener that the past perfect tense would have given.