That’s right, people . . . it’s one of those days when Dr. Doyle waxes, if not wroth, at least a little bit cranky about the latest writing-related pebble in her metaphorical sandal.
Okay, then. Listen up.
The phrase is not “free reign.” It’s “free rein.”
Why? Because it’s a horsemanship metaphor. In equestrian usage, “free rein” refers to a rein held loosely to allow a horse free motion, or to the freedom that doing so gives to the horse.
(It refers, in other words, not to having control or power over somebody or something, but to having self-determination or freedom of choice in a particular situation.)