Second Language Acquisition and Second Language Learning examines how adults develop competence in another language through subconscious acquisition and conscious study. Its central framework, Monitor Theory, treats learned grammar as a tool for checking language produced through acquired competence. The book distinguishes natural communication from explicit instruction, explaining why knowing grammatical rules does not automatically produce fluent speech. Successful monitoring requires time, attention to correctness, and knowledge of the relevant rule. These conditions help explain differences between learners who overuse grammatical checking, those who rarely use it, and those who apply it selectively in writing or prepared speech. The chapters connect this distinction to language aptitude, attitudes, motivation, and classroom environments. They examine grammatical morpheme studies, the relationship between adult and child acquisition patterns, and the circumstances in which conscious grammar changes performance. Another discussion interprets first language interference as reliance on existing knowledge when second language competence remains insufficient, highlighting the possible value of listening before speaking. Further sections explore neurological research, cerebral dominance, and proposed explanations for differences between children and adults. The contents also identify discussions of routines, patterns, simplified language, and the relationship between theory and teaching practice. Together, these investigations offer teachers and students of applied linguistics a focused account of how communication, formal knowledge, and learner characteristics interact in adult language development.