[As additional resources, links to book reviews and book purchasing information can be found beneath the quotations when this information is available.]
James Fillis recommended using a martingale only if the rider had reason to think that the horse threw his head about or carried it too high. Then, he recommended using only the standing or fixed martingale buckled on to the nose-band. He did not recommend the running or standing martingale attached to the rings of the snaffle as it effected the horse's mouth. "It [the martingale] ought to be long enough to allow the horse to carry his head high, and short enough to prevent him bringing his nose in a horizontal position."
"Some riders try with this instrument [the martingale] to prevent a horse from fighting the hand and throwing his head; but this is a big mistake, because it confirms, rather than corrects, this vice. This invention should be banned from good riding academies."