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I understand that sometimes the words omitted are not recoverable. But here are two I think show what the conjunction than is joining:

1a. You are more likely to train harder with a trainer than without.

Is this short for below?

1b. You are more likely to train harder with a trainer than you are likely to train harder without a trainer

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2a. This suggests that there were more people at the meeting than might have been expected.

Short for?

2b. This suggests that there were more people at the meeting than how many might have been expected.

I assume I don't need to include the repeated words in any context to show that the conjunction is joining equal parts. But let me know if you disagree.
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(1b) doesn't really work for me. I suppose it's clear enough what it's trying to say, but "You are more likely to ... than you are likely to ..." seems illogical.

(2b) seems wrong too (I mean, again it's clear what it's saying, but the English seems faulty). I wondered about "... than the number that might have been expected". To my ear this is much better, but still it doesn't seem exactly logical.
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Mr Wordy"You are more likely to ... than you are likely to ..." seems illogical.
It occurred to me later that 1b can theoretically be parsed with a structure like "You are more sad than angry". The two adjectives ("sad" and "angry" in my toy example) are then "likely to train harder with a trainer" and "likely to train harder without a trainer". I doubt this is what you intended though.
Mr WordyThe two adjectives ("sad" and "angry" in my toy example) are then "likely to train harder with a trainer" and "likely to train harder without a trainer". I doubt this is what you intended though.
Hi, I think you're spot on. 'than' isn't joining two clauses but two adjective phrases--'likely to train...with' and 'likely to train...without'

I've read that conjunctions are meant to join equal sentence parts. Words can be omitted, but recoverable.