This chapter is concerned with listing and analyzing some typical definitions of causation and examines various statements of the causal principle. Such an examination of definitions is indispensable in every rigorous approach to the causal problem and, indeed, in every scientific treatment of philosophic questions. The Aristotelian teaching of causes lasted in the official Western culture until the Renaissance. Modern thought, while retaining the externality of causation, has preferred other definitions of the efficient cause. The vagueness of the definitions of causal bond until about one century ago has prompted the framing of more precise, and consequently more schematic and abstract, formulations of the causal principle. The correlated variations of the elements in a structure fit the Humean formula of causation. The empiricist reduction of causation to regularity is grounded in the original sin of empiricism, namely, the identification of truth with its criterion, the reduction of the meaning of a proposition to the mode of its verification.