William Law, a member of the First Presidency of the LDS Church in Nauvoo, Illinois, became an apostate in 1844, shortly before Joseph Smith was murdered at Carthage. According to his own statements and actions, William Law had developed a genuine commitment to Mormonism before becoming a schismatic. However, by the spring of 1843 his commitment began to waver, and by early 1844 he had concluded that Joseph Smith was a fallen prophet. Some crucial comments regarding his apostasy were made in moments of tremendous fear and anger; others were offered after many years of reflection. This paper will attempt to identify the fundamental causes of William Law's apostasy.