Imagine a sailboat traveled from Oslo to Antarctica. One might infer from this that there was a pilot of the sailboat, who guided the process by which the boat arrived where it did, leveraging the natural processes when he could and the mechanical processes of the boat. Furthermore, one might infer that he intended to arrive there when he set out. So, you have coordination combined with intentionality.
A response to these inferences might be that we can explain the movement of the sailboat by reference to the tides, currents, wind, and the direction of the rudder on the boat and propulsion of the propeller – all natural or mechanistic causal explanations – without a captain or pilot. The destination was arrived at in a way by chance – the boat just happened to arrive where it did, propelled by these natural or mechanistic causes.
Yet, there might be parts of the journey where it seems unlikely the boat would be able to navigate simply based on these causal processes – perhaps there is a narrows, or any area with reefs, or pack ice, or perhaps the trajectory of the boat seems to require tacking. It might seem unlikely that the causal processes outlined above are sufficient to explain the traveling of the sailboat.
To this, one could say a ‘captain-of-the-gaps’ (or perhaps ‘captain-of-the-narrows’ is more apt) is being postulated, to help the boat get across terrain it seems unlikely to have been able to have traversed with the given repertoire of causal processes (current, wind, and so on). Yet, perhaps in the future we will discover circumstances that make it seem more likely that the repertoire is sufficient – perhaps the reefs weren’t as numerous as thought, and so on.
In this case, however, what I have in mind is not an imaginary one but rather an historical one, where the Norwegian expedition to the Antarctic, led by Roald Amundsen, traveled from Oslo to the Ross Ice Shelf. In this case, we know that the sailboat (the Fram) was guided by a captain, various steersmen, and so on, and that the natural forces of tide, wind, current and so on were important – necessary – parts of the story, but the entire story would be incomprehensible if left at that.
When developing a theory of how the boat got from one place to another, we might get progress by postulating currents, prevailing winds, and so on. We might therefore conclude that these will be sufficient to explain it. This is not a good argument. Rather, we have warrant for saying we have a part of the picture.