Abstract: This paper explores the speculative process based on transcendental space-time and the way back to language home in Reason. The speculative process on the Being of language is preconditioned by the unity of Being of Reason, through which the Being of language can be exhibited as the unity of its essence and its phenomenon; the language practice, as a subjective activity, is always a comprehensive application of its transcendental form under the condition of time and space; relying on the speculative process with the space-time form in the comprehensive application, reason can establish an absolute world of language beyond its phenomenon; as for the Being of language, the speculative reason concerns nothing about language's phenomenal, conditioned and experienced part, but its original, unconditioned and pure Being.