Edward L. Thorndike, answered from the texts and cited to the page.
The situation-response bond is the basic unit of all behavior and all learning. At any moment, the total state of affairs acting upon an animal — everything in its environment that has appreciable effect upon it — constitutes the situation; what the animal thinks, feels, or does as a result is the response.1 Bond is simply the name for the connection between them, formed in the nervous system, strengthened by satisfying consequences and weakened by annoying ones.
The notation S→R is convenient but requires careful reading. It is never a bond from the whole undivided situation to some single undivided act. All learning is analytic: the bond formed never leads from absolutely the entire state of affairs at the moment, and within any bond there are always minor bonds from parts of the situation to parts of the response, each with a certain degree of independence.2
The sensory neurones are analytical organs; different neurone groups pick out different elements of the situation, form preferential connections, and converge upon the response — not as an indissoluble unit but as a structured set of partial bonds.3 Write it properly and S→R expands into (S_a + S_b + S_c +...) → (R_a + R_b + R_c +...).4 What this means practically is that a bond, once formed, carries transfer with it.
If a part of the original situation recurs in a new context, that part of the response has a certain tendency to appear without its old accompaniments — which is precisely how learning generalizes without appeal to any mysterious faculty of reason.5 The chick that has learned a labyrinth of twenty-three associations goes straight through it without error; its learning is adequately accounted for as the strengthening and weakening of bonds between situations present to sense and responses in the nervous system, unmediated by ideas.6 That is the mechanism. Connection, consequence, and amount — nothing more is needed.
The total state of affairs by which an animal is at any given time influenced is called the stimulus or 'situation.' What he thinks or feels or does, as a result of this total state of affairs acting upon his nature, is called his total response to it.Education A First Book
All learning is analytic. (1) The bond formed never leads from absolutely the entire situation or state of affairs at the moment. (2) Within any bond formed there are always minor bonds from parts of the situation to parts of the response, each of which has a certain degree of independence.Educational Psychology Vol 2 The Psychology of Learning
Each total situation-response bond is composed of minor bonds from parts of the situation to parts of the response, because man's equipment of sensory neurones is such a set of analytical organs as it is, and because his connecting neurones are such a mechanism as they are for converging and distributing the currents of conduction set up in these sensory neurones.Educational Psychology Vol 2 The Psychology of Learning
The convenient custom of symbolizing a bond as S1→R1, or S2→R2 always requires interpretation as (S1a + S1b + S1c + S1d... S1n) → (R1a + R1b + R1c... R1n).Educational Psychology Vol 2 The Psychology of Learning
Within any bond formed there are always minor bonds from parts of the situation to parts of the response, each of which has a certain degree of independence, so that if that part of the situation occurs in a new context, that part of the response has a certain tendency to appear without its old accompaniments.Educational Psychology Briefer Course
The three cases of learning quoted are adequately accounted for as the strengthening and weakening of bonds between a situation present to sense and responses in the nervous system which issue then and there in movement.Educational Psychology Briefer Course