# Only if ... we can ...

#### VicentGiner

##### Member
I don't know if the following sentence can be said in English, I mean, whether the usual order of parts of a sentence can be swapped like this, or I should change something:

Notice that only if two events are independent we can express the probability of their intersection as the product of their respective probabilities.
Is it right? Thank you in advance.

• #### entangledbank

##### Senior Member
The 'if' clause can precede or follow the main clause:

If two events are independent, we multiply the probabilities.
We multiply the probabilities if the two events are independent.

However, 'only' behaves like a negative word. When it occurs at the beginning of a sentence, it causes the subject and auxiliary to be inverted:

If two events are independent, we can multiply the probabilities.
Only if two events are independent can we multiply the probabilities.

If two events are independent, we multiply the probabilities.
Only if two events are independent do we multiply the probabilities. [there wasn't an auxiliary to invert, so we have to add auxiliary 'do']

#### VicentGiner

##### Member
The 'if' clause can precede or follow the main clause:

If two events are independent, we multiply the probabilities.
We multiply the probabilities if the two events are independent.

However, 'only' behaves like a negative word. When it occurs at the beginning of a sentence, it causes the subject and auxiliary to be inverted:

If two events are independent, we can multiply the probabilities.
Only if two events are independent can we multiply the probabilities.

If two events are independent, we multiply the probabilities.
Only if two events are independent do we multiply the probabilities. [there wasn't an auxiliary to invert, so we have to add auxiliary 'do']
Wow!! Thank you very much!!!

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