Reasoning that starts with a given set premises and draws a conclusion is called deductive reasoning. Reasoning that draws a general conclusion based on a set of examples is called inductive reasoning. So deductive reasoning goes from general principles to specific conclusions and inductive reasoning goes from specific principles to general conclusions. Both of these types of logic are used in science.
Inductive and Deductive reasoning are different and even opposite concepts but in practice deductive and inductive reasoning are often used together even without knowing it. For example one may be drawing a general conclusion form observed evidence (induction) based on general principles called assumptions. (deduction)
Mistakes in reasoning called Logical fallacies are some times made. This can happen both deliberately and accidentally. The important thing is to avoid them since they resultant in erroneous conclusions.