What is the difference between "only for as long as" and "only if"?


  • A coral reef will continues to exist only for as long as it can expand at a faster rate than it is being destroyed.
  • Annual subscription options allow you to commit to a contract only for as long as you need it.
  • Children are admitted only if accompanied by an adult.
  • The lawyer is paid only if he wins.

I am learning toward "only for as long as". It seems like that there is no difference between "only for as long as" and "only if". Is it right? If so, which one is more well-used expression?

This is the first time I post questions here! So, if there is some problem in this question, please comment to me.


"Only for as long as" - this is (probably) an ongoing process but the condition indicates how long it will last.

"Only if" - the condition indicates whether or not the statement is true.

The first is a matter of time, whether the second is a matter of being true or false.

(If you are a programmer, it's a case of while vs if!)

  • Thanks for the nice explanation! The last line you wrote was really helpful. – K.Oh Oct 21 '16 at 10:42

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