Since, in modern times, Calvinism is generally associated with compatibilism, and since that term is frequently used at T-blog, it might be helpful to offer some basic definitions. According to classical compatibilism:
“To be free, most compatibilists have insisted, means in ordinary language (1) to have the *power* or *ability* to do what we will (desire or choose) to do, and this entails (2) the absence of *constraints* or *impediments* preventing us from doing what we will, desire, or choose. The constraints or impediments they have in mind include physical restraints, lack of opportunity, duress or coercion, physical or mental impairment, and the like.”
“What do they say about the freedom *to do otherwise*? It is also defined by classical compatibilists in terms of (1) and (2). You are free to do otherwise than meet your friend when you (1) have the power or ability to avoid meeting him, and which entails in turn that (2) there are no constraints or impediments preventing you from avoiding the meeting (e.g., no one is forcing you at gunpoint to meet him)."
"It does mean you *would* do it, *if* you wanted or desired to do it. Thus they hold that (1) and (2) entail a third feature of classical compatibilism, namely, that terms such as *can*, *power*, *ability*, and *freedom* should be given a *conditional* or *hypothetical* analysis: (3) that an agent can (has the power, is able, is free, to) do something means that the agent would do it, if the agent wanted (or desired or chose) to do it."
“To say ‘you could have done otherwise’ would only amount to the counterfactual claim that you would have done otherwise, if (contrary to fact) the past (or the laws) had been different in some way, for example, if you had wanted or desired or chosen otherwise."
R. Kane, ed. The Oxford Handbook of Free Will (Oxford 2002), 12-13.
Contemporary compatibilism has developed a number of further refinements, but that's a place to start.