In such a purely instinctive action as leaping backwards from a falling stone, the impulse to leap and the inference that there is danger, are simply two names for a single automatic and unconscious process.

We can speak of instinctive inference as well as of instinctive impulse; we draw, for instance, by an instinctive mental process, inferences as to the distance and solidity of objects from the movements of our eye-muscles in focussing, and from the difference between the images on our two retinas.

We are unaware of the method by which we arrive at these inferences, and even when we know that the double photograph in the stereoscope is flat, or that the conjurer has placed two converging sheets of looking-glass beneath his table, we can only say that the photograph 'looks' solid, or that we 'seem' to see right under the table.
The whole process of inference, rational or non-rational, is indeed built up from the primary fact that one mental state may call up another, either because the two have been associated together in the history of the individual, or because a connection between the two has proved useful in the history of the race.

If a man and his dog stroll together down the street they turn to the right hand or the left, hesitate or hurry in crossing the road, recognise and act upon the bicycle bell and the cabman's shout, by using the same process of inference to guide the same group of impulses.

Their inferences are for the most part effortless, though sometimes they will both be seen to pause until they have settled some point by wordless deliberation.