This document discusses different theories and conceptions of teaching. It describes the shift from a focus on methods in the 20th century to a more complex view of language pedagogy in the 21st century. It outlines three main conceptions of teaching: 1) science-research conceptions which view teaching as applying principles from research, 2) theory-philosophy conceptions which are based on educational theories, and 3) art-craft conceptions which treat each teaching situation uniquely based on its characteristics. The document advocates for an approach to teaching that involves diagnosis of learners' needs, treatment through appropriate activities and techniques, and assessment to evaluate learning.