Definition from Wiktionary, the free dictionary
- Not unless; used to introduce a necessary condition.
- The company will succeed only if it has sufficient backing.
- 1611, Bible (KJV), Kings-Chapter-21/#8 2 Kings 21:8:
- Neither will I make the feet of Israel move any more out of the land which I gave their fathers; only if they will observe to do according to all that I have commanded them, and according to all the law that my servant Moses commanded them.
- 1965 June 4, John W. Tukey, Data Analysis and the Frontiers of Geophysics, in Science New Series, 148(3675), page 1288, 
- This is a somewhat paradoxical conclusion, and we can be happy to learn that it follows only if we can trust, precisely and in detail, the assumed way in which the probability of occurrence of a deviation decreases as the size of that deviation increases.
- 2005, Ellen Siever, Aaron Weber, Stephen Figgins, Robert Love & Arnold Robbins, Linux in a Nutshell, O'Reilly, page 802
- This option is available only if the client supports it.
- This term often implies that the condition is not only necessary, but also sufficient. To avoid this implication, or rather to use this implication to avoid ambiguity, an additional hedge may be added to the main clause (apodosis): "The company can succeed only if it has sufficient backing."
- When the subordinate clause (protasis) follows the main clause, the word only may be moved earlier inside the main clause, with the if remaining at the start of the subordinate clause: "The company will only succeed if it has sufficient backing".
- When the subordinate clause precedes the main clause, the verb in the main clause undergoes inversion (as with other uses of only): "Only if the company has sufficient backing will it succeed."