Agabus

i) One of the disputes between cessationists and charismatics is whether there's such a thing as fallible prophecy. Charismatics cite Agabus (Acts 21:1-14) as an example of fallible prophecy. 

There's a sense in which I think both sides are wrong. I think allegations that Agabus was inaccurate are very wooden, but I'd like to approach the issue from a different angle. In some cases, a prophet can be right even though events didn't turn out as predicted. Is that paradoxical? Not really.

ii) To begin with, some prophecies are conditional. That's common regarding oracles of judgment. A paradigm case is Jer 18:7-11:

7 If at any time I declare concerning a nation or a kingdom, that I will pluck up and break down and destroy it, 8 and if that nation, concerning which I have spoken, turns from its evil, I will relent of the disaster that I intended to do to it. 9 And if at any time I declare concerning a nation or a kingdom that I will build and plant it, 10 and if it does evil in my sight, not listening to my voice, then I will relent of the good that I had intended to do to it. 11 Now, therefore, say to the men of Judah and the inhabitants of Jerusalem: ‘Thus says the Lord, Behold, I am shaping disaster against you and devising a plan against you. Return, every one from his evil way, and amend your ways and your deeds.’

In this case, the prediction is not a statement of what will happen without further ado, but what will happen unless sinners repent in response to the fearful warning. 

That in turn goes to a general principle. Some predictions envision a future if the recipient does nothing different. Take a premonition. Suppose I have a premonitory dream. Suppose it has a dire denouement. 

When I wake up, and events begin to repeat themselves, just like I saw in my dream, I take actions to change a key variable, resulting in a different outcome that diverts the stream of causality, with a different end-result. 

Was the premonition false? In one sense, I'll never know, since I deliberately thwarted that trajectory. 

But what if the purpose of the premonition was to forewarn me so that I could take steps to avert that outcome? There were two futures in play: one in which I go with the flow and one in which I divert the flow. Which future is actual and which is counterfactual depends on what I do in response to the premonition. 

BTW, that's consistent with Calvinism and freewill theism alike. This goes to the difference between predestination and fatalism. If I act on the premonition to avoid the future I see in the dream, I'm doing what I was predestined to do. The dream is a stimulus to that end. The premonition, as well as my reaction, was included in God's plan, as a means of advancing the plot to the appointed goal. Although the premonition doesn't contain my reaction to the premonition, that's contained in God's plan, like Russian dolls, where smaller factors are nested in larger factors. 

iii) This, in turn, goes to the distinction between foreknowledge and counterfactual knowledge. If what I see in the dream plays out, then it was foreknowledge. 

But if I heed the premonition by changing a variable in the chain of events leading up to the dire outcome to deflect that outcome, then it was counterfactual knowledge. In a proximate sense, my action determines whether it was foreknowledge or counterfactual knowledge–rather like Schrödinger's cat, although there's another sense in which my action is predetermined by the dream. Having been tipped off, I act differently than if I never had that advance knowledge. 

iv) Returning to the original illustration, because Paul was forearmed by the prophecy of Agabus, he may have handled some situations differently than if he wasn't privy to that foresight. In consequence, even assuming that things didn't unfold in quite the way Agabus envisioned, his prophecy could still be infallible if that was a prediction about an alternate timeline. That's exactly the fate which awaited Paul, if Agabus hadn't shared his vision with Paul. But knowing the prophecy could affect Paul's actions in many subtle ways. He might adjust his plans in ways that had the same general, ultimate outcome, but by a somewhat different route. 

v) However, this only applies to predictions where the recipient has some control over the relevant variables. There are, of course, predictions that are out of our hands, like natural disasters, which we lack the wherewithal to stop. In some cases, a recipient might have the power to redirect the course of events if he only knew all the intervening causes and altered one of them.