There were three laws of returns mentioned in the history of economic thought up till Alfred Marshall's time. These laws were
i)the laws of increasing returns,
ii) diminishing returns and
iii)constant returns.
According to Dr. Marshall, the law of diminishing returns applies to agriculture and the law of increasing returns to industry. Much time was wasted in discussion of this issue. However, it was later on recognized that there are not three laws of production. It is only one law of production which has three phases, increasing, diminishing and negative production. This general law of production was named as the Law of Variable Proportions or the Law of Non-Proportional Returns.
The Law of Variable Proportions which is the new name of the famous law of Diminishing Returns has been defined by Stigler in the following words:
As equal increments of one input are added, the inputs of other productive services being held constant, beyond a certain point, the resulting increments of produce will decrease i.e., the marginal product(MP) will diminish.
According to Samuelson:
An increase in some inputs relative to other fixed inputs wills, in a given state of technology cause output to increase, but after a point, the extra output resulting from the same addition of extra inputs will become less
marto answered the question on April 16, 2019 at 12:43