Puzzling prepositional phrases

[qinhh76]

I'm doing research on pairs of near-synonymous prepositional phrases but very puzzled by the nuances of the following pairs, which are all from BNC (British National Corpus). Looking forward to your insights.

(1) a. We stood up and left the house by the back door.
b. He entered the house through the back door.

(2) a. All such grafts will die from lack of water.
b. Farmers are losing crops for lack of water.

(3) a. By conservative estimates, 2.5 million people around the world die each year from smoking cigarettes.
b. The same thing that's happened in Ireland has happened all over the world.

[qinhh76]

Who can help me？

[Cantabrigian]

Hello,

Well, this data is not very surprising. What exactly is your question?

[Raymott]

Hello,

Well, this data is not very surprising. What exactly is your question?

I think his question is quite clear:
Would you please explain the different nuances of using the alternative prepositions in the example sentences?

I cannot see any difference worth explicating. They mean essentially the same thing.

[qinhh76]

Having reflected on this puzzle for quite a few days, here is my thoughts:

The means-passage distinction: by vs. through
By and through can both express the spatial conception of “passage” and metaphorical meaning “by means of”. Without a context, their meanings can be ambiguous. Quirk et al. (1985: 699) hold that by in the following example expresses “means”:
The thief must have entered and left the house by (=through) the back door.
Lindstromberg (1998: 147) also argues:
“Sometimes by seems to mean ‘through’:
Come in by the side door. The others are locked.
However, such uses of by very likely derive form its use as an indicator of means. So, the most conceptually accurate paraphrase of by in [the above sentence] is not ‘through’ but rather something like ‘using X as a route’.”
Judging from the above claims, we can conclude that by in such context is more metaphorical (i.e. donating “by means of”) than spatial (i.e. meaning “through”). It can also be observed that both of the claims use through (more spatial) to explain by, which does not mean they can be treated on the equal footing. As a matter of fact, the semantic overlap between by- and through- phrase may intersect from different domains. The following sentences are examples of reification of experience:
a. We stood up and left the house by the back door.
b. He entered the house through the back door.
Either of the PPs could describe the same incident, but there can be a difference in construal. In (a), by the back door means “by means of the back door”. In (b), through the back door implies “physically in and then out of the back door”.

[qinhh76]

Do you agree with my thoughts? You are simply welcome to join in the argument!

[Tdol]

It depends- in the example of the thief, I would agree that it could have a meaning of 'by means of', but in the 'We stood up' example, I can't see much of a case for it unless there were some special restrictions or something unusual about using the back door. Thieves can come in through the doors, windows, down the chimney,etc, which is different from the way most people come in or leave a building.

Without further context, I see no real difference between :
We stood up and left the house by the back door.
and We stood up and left the house through the back door.

[Raymott]

Having reflected on this puzzle for quite a few days, here is my thoughts:

The means-passage distinction: by vs. through
By and through can both express the spatial conception of “passage” and metaphorical meaning “by means of”. Without a context, their meanings can be ambiguous. Quirk et al. (1985: 699) hold that by in the following example expresses “means”:
The thief must have entered and left the house by (=through) the back door.
Lindstromberg (1998: 147) also argues:
“Sometimes by seems to mean ‘through’:
Come in by the side door. The others are locked.
However, such uses of by very likely derive form its use as an indicator of means. So, the most conceptually accurate paraphrase of by in [the above sentence] is not ‘through’ but rather something like ‘using X as a route’.”
Judging from the above claims, we can conclude that by in such context is more metaphorical (i.e. donating “by means of”) than spatial (i.e. meaning “through”). It can also be observed that both of the claims use through (more spatial) to explain by, which does not mean they can be treated on the equal footing. As a matter of fact, the semantic overlap between by- and through- phrase may intersect from different domains. The following sentences are examples of reification of experience:
a. We stood up and left the house by the back door.
b. He entered the house through the back door.
Either of the PPs could describe the same incident, but there can be a difference in construal. In (a), by the back door means “by means of the back door”. In (b), through the back door implies “physically in and then out of the back door”.

I agree that 'through' is more concrete, and 'by' more metaphorical, as you have explained - in this context.
However, consider:
He achieved his goal through hard work and perseverance.
Here, you will see that 'through' is a less concrete choice then 'by'.

This is consistent with Tdol's "no real difference" and my "essentially the same thing".