"If" is a song written by David A. Gates, from their 1971 album Manna, which is a perennial favorite at weddings (for example, as a first dance song) ever since it was released.
http://en.wikipedia.org/wiki/If_(song)
http://en.wikipedia.org/wiki/Manna_(album)
http://en.wikipedia.org/wiki/Bread
https://en.wikipedia.org/wiki/Olivia_Newton-John
http://en.wikipedia.org/wiki/If_(song)
http://en.wikipedia.org/wiki/Manna_(album)
http://en.wikipedia.org/wiki/Bread
https://en.wikipedia.org/wiki/Olivia_Newton-John
Text to this post, obtained from this song's Wikipedia page, has been slightly modified and made available here under the Creative Commons Attribution-ShareAlike 3.0 Unported License. (CC BY-SA 3.0)
https://creativecommons.org/licenses/by-sa/3.0/