In everyday constructions such as those that the OP presents, when may be used in either of two senses:
on a particular occasion that
or
on every occasion that
The sense of when that the speaker intends is necessarily contextual, and the meaning that a hearer attributes to the speaker's words in everyday situations may at times involve some rather subtle distinctions. Our default handling of a single past event is to use when plus a simple past tense, as in the OP's second example:
When I paid her one dollar, she answered my question.
If we want to describe a recurring situation in the past, our usual tactic is to change when to whenever:
Whenever I paid her one dollar, she answered my question.
However, the OP's first example
When Jack did all the shopping, he went to the café.
doesn't follow this normal pattern. Here our tendency (as hearers or readers) is to understand when to mean "on every occasion that" (that is, "whenever") rather than "on a particular occasion that." I suspect that the reason we shift to the "whenever" understanding of when in this case is, in large part, that the cause-and-effect relationship between "Jack did all the shopping" and "he went to the café" is far more tenuous than the one between "when I paid her one dollar" and "she answered my question." Jack did all the shopping and then he went to the café, but the first event didn't cause the second one; instead, the second event simply followed (sequentially) the first one.
Typically when we describe an event that follows a previous event without involving a cause-and-effect connection to that prior event, we use the word after, not when. Thus we would normally describe a one-off sequence of shopping + café visit this way:
After Jack did all the shopping, he went to the café.
Under these circumstances, the speaker's choice of when instead of after leads us to infer that the speaker has in mind a continuing pattern of behavior, rather than a one-time-only occurrence. We conclude that when means whenever.
To test this theory of how English speakers understand when, let's consider another example involving Jack the shopper, but this time let's tie his sequential actions more closely together. Here is the new example:
When Jack did all the shopping, the clerk double-bagged the groceries.
Here the double-bagging follows from the shopping much more closely than the café visit in the earlier example did. Consequently a hearer may be more inclined to interpret the sentence as describing a once-only event. Indeed, if we get rid of the troublesome word all, a hearer is extremely likely to interpret it that way:
When Jack did the shopping, the clerk double-bagged the groceries.
The all muddies the waters by implying that more than one instance of shopping is involved, which makes the "on a particular occasion that" interpretation of when at least a little more difficult to sustain.
From this, it follows that the presence of all in the original example involving Jack's shopping and the subsequent café visit may have provided a subtle but important cue to hearers that the speaker was using when in the sense of "whenever." The presence of all, combined with the weak cause-and-effect relationship between shopping and café lounging, prompts a shift in our interpretation of when from the default "on a particular occasion that" to the less common alternative "on every occasion that."
No; or rather, only in exactly the same way as it’s ‘necessary’ to put a comma before an ‘as clause’ like the one in your example.
Formal writing or not, in modern English, at least, most commas are optional.
My limited experience of it is that Cambridge is one of the worst English dictionaries available, which is why almost no-one living in England has heard of it.
Prove this for yourself by comparing anything of which you are not certain to Oxford or Webster, for instance. Not in my but in your view, which is better?
With or without any comma, ‘I hope they’ve decided to come as I wanted to hear about their India trip’ throws up at least three questions which might not be truly important in or of themselves, but as evidence for the reliability of a dictionary, cut about as much mustard as a dead, red herring. At best, that sentence is unnatural; it’s rather clearly not a quoted but an artificially constructed example, and not a good one.
In the same way ‘Sean had no reason to take a taxi since his flat was near enough to walk to’ is wholly comprehensible, but was it supposed to be merely comprehensible, or intended to give a clear and helpful illustration of a specific point, while at the same raising no irrelevant questions?
Best Answer
As you noted, participle phrases can be used for a number of reasons. Besides what you listed, they could also show simultaneous action:
Your concern is that one use implies cause-and-effect:
Swapping the order of phrases has little effect on the participle phrases that showed a reason for an action or simultaneous action ("She skipped down the sidewalk, whistling joyfully"). But it's understandable that you would hesitate to invert the cause-and-effect example, putting the effect before the cause:
However, this is not so much a violation of a grammatical rule; it's simply cumbersome and difficult to understand. Yes, you could invert these sentences as well, you just might not want to.