will you be able to see the spots on the sun

[taraa]

Why is reversion used in the second part not in the first?

Only if you look through this dark glass will you be able to see the spots on the sun. (from a Persian book)

 

[puli_dog]

I'm not sure, but I feel that an inversion in the first part would suggest that, amongst different dark glasses, this particular would be the one to employ, or else "without adding anything to the dark glass"...

 

[grassy]

Why is reversion inversion used in the second part not in the first?

Only if you look through this dark glass will you be able to see the spots on the sun. (from a Persian book)

Becuase inversion applies to the main clause.

 

[taraa]

Many thanks both.

Becuase inversion applies to the main clause.

Interesting.

 

[taraa]

Is here again the second one the main clause?

Not until she took up rock climbing did she overcome her fear of heights

 

[grassy]

Yes. She overcame her fear of heights when she took up rock climbing.

 

[PaulQ]

Only if you look through this dark glass will you be able to see the spots on the sun.
Not until she took up rock climbing did she overcome her fear of heights

Inversion is often used after a fronting, adverbial, negative time phrase/clause:

Not in all my days have I seen such a thing!
Hardly had I closed the door.
No more will I go a-roving.
No longer did he take the dog walking.
Rarely is there blossom at this time of year.
etc.

 

[taraa]

Great. Many thanks to you both.

 

[Jektor]

The inversion here emphasises the part which is moved to the beginning of the sentence:
"You will only be able to see the spots on the sun if you look through this dark glass" - no emphasis.
"Only if you look through this dark glass will you be able to see the spots on the sun" - the inversion emphasises that the effect will only happen if you first place the dark glass in front of your eye.
"Not until she took up rock climbing did she overcome her fear of heights" - the inversion emphasises the fact that she only overcame her fear of heights by first taking up rock climbing.
wordreference.com - careful-as-she-is-she-had-an-accident.2895005
etc..
.

 

[taraa]

The inversion here emphasises the part which is moved to the beginning of the sentence:
"You will only be able to see the spots on the sun if you look through this dark glass" - no emphasis.
"Only if you look through this dark glass will you be able to see the spots on the sun" - the inversion emphasises that the effect will only happen if you first place the dark glass in front of your eye.
"Not until she took up rock climbing did she overcome her fear of heights" - the inversion emphasises the fact that she only overcame her fear of heights by first taking up rock climbing.
wordreference.com - careful-as-she-is-she-had-an-accident.2895005
etc..
.

Many thanks for the great explanation.