Abstract: Systems, methods, and devices for second language acquisition, using incrementally increasing in-line word and grammar substitution to increase comprehension and retention by presenting new material in an already-understood context. The systems, methods, and devices may be implemented in a range of embodiments, from books to computer systems, and generally use isolated word and phrase substitution with a translated word/phrase in the context of a base language document to convey the meaning of the translated word/phrase to the user by context.