Question

Who has propounded the law of trial and error of learning

Answer 1

The term trial-and-error learning was devised by C. Lloyd Morgan. Edward Thorndike showed the way a trial-and-error experiment could be managed in the laboratory. Thorndike observed that learning occurs as a result of associations formed between stimuli and responses.

Learning by trial and error refers to the phenomenon where learning occurs after repeated trials. It is a fundamental method of problem solving. 

Answer 2

The answer of your question is " C. Lloyd Morgan " He was the first man who propounded this law of trial and error. But This was the "Edward Torndike" who experimentally proof this law by making the trials on a cat. He observed that whenever the positive result occur, there is learning occur. 
This law states that after the trial again and again or facing the situation, learning is the end result and for the problem solving method the attempts are made repeatedly until the end result is success .