This article argues that previous attempts to explain SLA should not be disregarded. Instead, when they are put together, they provide a broader and deeper view of the acquisition process. There is evidence to support the claim that second language acquisition (SLA) is a complex adaptive system due to its inherent ability to adapt to different conditions present in both internal and external environments. Based on this understanding, widely discussed second language theories, including behaviorism, will be treated as explanations of parts of a whole, since each captures a different aspect of SLA. In order to justify this assumption, excerpts from some English language learning histories are provided to exemplify how learners describe their learning processes. The final claim is that SLA should be seen as a chaotic/complex system.