Use of would have been as perfect conditional

Question

If we do not have any factual evidence about an event occurred in the past, we can use perfect conditional to express our inference about it based on from our knowledge and information.

I often use "It seems", or "in most likelihood", but not would have to tell the past which I am not completely sure. Can you help me with an explanation to understand the usage of would have as perfect conditional?

1. The Roman readers, many of whom would at one time have been in the army, would have had no trouble with Caesar's austere narrative; they would have found it complete as it is. They would have known how to read the shorthand. -V S Naipaul

What changes will occur if I replace would have with the simple past?

2. Yesterday my mother went to market so she had the chance to see the accident.
   Yesterday my mother would have gone to market so she would have had the chance to see the accident.

What difference does the use of perfect conditional bring here?

I am familiar with the usage of "would have" with an if clause. But I have not found the usage of "would have" as perfect conditional very frequently. But, Naipaul uses it extensively in his book while describing even the well-known events of the Roman history. It startles me. Many historical events are just logical inferences, reconstructions. We know a very few complete fact about the remote past. But the history books are not replete with the perfect conditional "would have".

Answer 1

The reason this use of "would have" is rare is that authors rarely need to use it. Often the simple past is sufficient.

The Roman readers, many of whom had been in the army, likely had little trouble with Caesar's austere narrative and found it complete as it is. They knew how to read the shorthand.

There's nothing really wrong with the repeated use of "would have", at least not for a single sentence or paragraph, but it would be disconcerting if used in every sentence. "Would have" implies uncertainty, and an expert on a topic should be more certain when writing about it. The occasional guess is fine, but an entire book of guesses is not.

Your example with your mother is 100% correct, in that you extrapolate a logical conclusion from a hypothetical past event. Another example:

Yesterday was a national holiday, so most of the stores would have been closed.

You would only use this tense if it had some relation to a current event, or some topic you're discussing:

Because of the holiday, most of the shops would have been closed, and my mother wouldn't have been able to buy groceries. So I don't know what we're going to eat if we go visit her today.

Yesterday my mother would have gone to market so she would have had the chance to see the accident. We should ask if she knows anything about it.

Caesar's narrative may seem overly terse and vague to the modern reader, but to the Roman readers, who would have served in the army, it would have been perfectly comprehensible.

Otherwise the simple past, perhaps with some expression of uncertainty, is usually fine:

Yesterday was a national holiday, so I think the stores were all closed.