In addition to the technical and experimental skills in daily lab work and a profound knowledge of one's professional field, chemical researchers need competence in analysing and interpreting their acquired experimental data in view of the claims they made in their research hypotheses. Both making proper hypotheses and interpreting data in a scientific manner are topics in this chapter. First, it will introduce the most important concepts of logic that play a role in scientific thinking and reasoning: Deduction, induction, and abduction. More important than the correct application of logic concepts is the awareness of pitfalls, biases and fallacies. Then, we will learn how logic informs the heart of the scientific method, the predictive power of proper hypotheses and the explanatory power of data analysis and interpretation. Furthermore, a subsection is dedicated to heuristic and methodological analysis. Last but not least, it is worthwhile having a closer look at statistical analysis and the differences between frequentist and Bayesian approaches. The goal of such a chapter in a book on good chemistry is, of course, a higher awareness of factors that determine the consistency and plausibility of scientific claims.