Why does this lesson show apparaître as an exception to the rule when the past particple is apparu?

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Accepted Answer

Hi Shelley,
The lesson on 'apparaître' is still being prepared but I will try to answer your question here-
In the sense of 'to appear' as in an event you can actually use both. You will hear "Le soleil est finalement apparu cet après-midi." or "Le soleil a finalement apparu... "The sun finally made an appearance this afternoon.)
The difference being emphasis on the action (using 'avoir') or the result (using 'être').
It is indeed a very subtle distinction and I would not worry too much about it ...
e.g
Les documents sont apparus/ont apparu ce matin. 
The documents appeared/materialised  this morning.
both are possible.
Hope this helps!

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I think it's because the passé composé of apparaître is normally formed with être instead of avoir.
(There should be a link to a lesson that explains that, but it seems to be broken.)

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Thank you for the quick response, Alan. I was not thinking about the auxiliary verb. I hope that the link to the lesson that explains that can be restored because apparaître is sometimes conjugated with être and sometimes with avoir, but I am not clear about the different circumstances.

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This is very helpful, thank you! I look forward to studying the lesson on "apparaître" when it is completed, as I find that the explanations (and examples) that you and your team produce are very  clear and easy to understand, as well as very thorough.

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So the reason of being an exception isn't a past participle form.