Edward L. Thorndike, answered from the texts and cited to the page.
The law of effect is important because it is the fundamental mechanism by which any organism — crab, dog, cat, child, or man of science — actually changes its behavior in response to experience. Without it, there is no learning; with it, there is no need to invoke mysterious inner faculties to explain how learning occurs. Put it plainly: of the many responses an organism makes to a situation, those followed by a satisfying state of affairs grow stronger, and those followed by an annoying state of affairs grow weaker.1
That is the whole engine. The cat clawing at the latch, the baby learning to smile at the bottle, the billiards player refining his stroke, the scientist preserving the idea that promises and discarding the one that does not — all of these are the same law at work at different levels of complexity.2 The crab choosing the path that brought food, the dog avoiding the box that brought shock — these are not different phenomena requiring different explanations; they are one phenomenon, measured in different organisms.3
The intimacy of the connection matters as well. The same degree of satisfyingness acts more strongly on a bond formed two seconds ago than on one formed two minutes ago, and more strongly when the situation and response were attended to closely.4 This is not a vague generality; it is a quantitative relationship, and it tells the teacher exactly where to place the reward relative to the act.
What makes the law foundational rather than merely useful is that it is the original force behind everything we call nurture, training, learning by experience, or intelligence itself.5 Strip away those grand words and you find, underneath each of them, connections being strengthened by satisfying consequences and weakened by annoying ones. The law does not describe one kind of learning among others; it describes the mechanism by which all modifiable connections are modified.
Education, industry, government, religion — every enterprise that sets out to change what men do operates, whether it knows it or not, by this law.6 Know it explicitly, and you can use it deliberately. Ignore it, and you use it blindly, with all the waste that blindness brings.
To the situation, 'a modifiable connection being made by him between an S and an R and being accompanied or followed by a satisfying state of affairs' man responds, other things being equal, by an increase in the strength of that connection. To a connection similar, save that an annoying state of affairs goes with or follows it, man responds, other things being equal, by a decrease in the strength of the connection.Educational Psychology Briefer Course
By it babies learn to smile at the sight of the bottle or the kind attendant, and to manipulate spoon and fork; by it the player at billiards or golf improves his game; by it the man of science preserves those ideas that satisfy him by their promise, and discards futile fancies.Education A First Book
By it a crab learns to respond to the situation, two paths, by taking the one, choice of which has in the past brought food. By it a dog will learn to respond to the situation, a white box and a black box, by neglecting the latter if opening it in the past has been promptly followed by an electric shock.Education A First Book
The strengthening effect of satisfyingness varies with its intimacy with the bond in question as well as with the degree of satisfyingness... the same degree of satisfyingness will act more strongly on a bond made two seconds previously than on one made two minutes previously.Educational Psychology Briefer Course
They are the effective original forces in what has variously been called nurture, training, learning by experience, or intelligence.Educational Psychology Briefer Course
It is the great weapon of all who wish in industry, trade, government, religion or education to change men's responses, either by reinforcing old and adding new ones, or by getting rid of those that are undesirable.Education A First Book