Abstract: The word ‘logic’ has many senses. Here we will understand it as meaning an account of what follows from what and why. With contemporary methodology, logic in this sense—though it may not always have been thought of in this way—is a branch of applied mathematics. This has various implications for how one understands a number of issues concerning validity. In this talk I will explain this perspective of logic, and explore some of its consequences with respect to the notion of logical form.