Negative-polarity adverbs and inversion sentences

Question

I asked a question here: Some questions about Inversion sentences

Now, I know that certain negative-polarity adverbs with the main adverb are what triggers inversion, like "not only", "only when", "only after", "not until", and etc.

I just wonder what about sentences like below. The negative-polarity adverbs in them trigger inversion? or These sentences are fine? (I am sorry if this has been answered in my previous post. Because my English is not good enough to know if this has been answered or not. )

When he only eats chips, he gets fat.

When I only do simple things, I can concentrate.

When a man only thinks of himself, he loses his friends.

Answer 1

The sentences are fine, and to refer to your previous question, the book is right in that the inversion is only required when the negative polarity adverbs to modify the entire clause. In your cases, they don't.

When he only eats chips, he gets fat.

Only when he eats chips does he get fat.

In the first sentence, "only" modifies "eats chips", while in the second sentence "only" modifies the entire clause, including "when". The two sentences differ in meaning, too:

When I only do X, Y happens.

means "Y happens at any time I do nothing but X". "When I only eat chips, I get fat" - if I eat nothing but chips, I get fat (but I can also get fat by other means, like eating only hamburgers).

Only when I do X does Y happen.

means "Y happens when I do X, and doesn't happen when I don't do X". "Only when I eat chips do I get fat" - to get fat, I need to eat chips, and no other food or activity makes me get fat.