The correct spelling of the phrase is free rein, not free reign. The latter spelling is a common error, and it almost makes sense given reign‘s meaning (i.e., the exercise of sovereign power). Plus, the misspelling is so common that we almost have to accept it as an alternative form. But free rein, an allusion to horseback riding, is the original form. The OED lists instances from as long ago as the 17th century.1 And as the Ngram at the bottom of this post shows, free reign is newer.
Examples
In poorly edited blogs and news outlets, free reign is the more common spelling—for example:
And really, what player doesn’t want to go all Simon Cowell on a teammate every now and then if given free reign? [MLB.com]
You can either give kids free reign with designing their play mat or set them up with a challenge. [Patch]
Incumbent political heads across the region are taking notice while the nervousness has given crude a free reign to head north. [MarketWatch]
But most edited publications use free rein—for example:
One part of that pact has already been exposed as flawed, since it turns out that, given a free rein, banks sometimes blow themselves up. [The Economist]
It seems that advertising companies are given free rein to make the cleverest, funniest ads of the year specifically to air during this one football game. [Guardian]
Julia Gillard took the debate to a lower level before the election when she invited people to give their prejudices free rein. [Sydney Morning Herald]
The second part of this sergeant’s letter calls for yet another vow. It reminds us that war, by its nature, breeds corruption and gives free rein to abuses of all sorts. [The Nation]
Ngram
The below Ngram charts the phrases’ use in English books published from 1800 to 2000. It shows the misspelling gaining ground.
