What is the role of practical thought in determining the intentional action that is performed? Donald Davidson’s influential answer to this question is that thought plays an efficient-causal role: intentional actions are those events that have the correct causal pedigree in the agent's beliefs and desires. But the Causal Theory of Action has always been plagued with the problem of “deviant causal chains,” in which the right action is caused by the right mental state but in the wrong way. This paper addresses an alternative approach to understanding intentional action inspired by G.E.M. Anscombe, interpreting that view as casting practical thought in the role of formal rather than efficient cause of action and thereby avoiding the problem of deviant (efficient) causal chains. Specifically, on the neo-Anscombean view, it is the agent’s “practical knowledge” – non-observational, non-inferential knowledge of what one is doing – that confers the form of intentional action on an event and is the contribution of thought to determining what is intentionally done. This paper argues that the Anscombean view is subject to its own problematic type of deviance: deviant formal causation. What we know non-observationally about what we are doing often includes more than what we intend to be doing; we also know that we are bringing about the foreseen side effects of acting in the intended way. It is argued that the neo-Anscombean view faces difficulty in excluding the expected side effects from the specification of what is intentionally done, whereas the Causal Theory has no such difficulty. Thus, the discussion amounts to an argument in favor of the Causal Theory of Action.