Sherlock Holmes had learned many reasoning skills and methods, including: Deductive reasoning: To deduce possible conclusions or truths by observing known facts. Inductive reasoning: Inferring a new conclusion or truth by observing known facts or patterns. 3. Combination of deduction and induction: By using deduction and induction at the same time, a more accurate answer can be obtained. 4. Analogy: Inferring possible situations or things by observing similar situations or things. 5. Consecutive reasoning: Inferring possible conclusions or truths by observing conditions and constraints. 6. Model Inference: Inferring possible conclusions or truths by establishing models or assumptions. These reasoning skills and methods were widely used in Sherlock Holmes 'case to help him come up with various complicated truths.