Returns to a factor means keeping other inputs constant, the change in physical output by increasing only one physical input. 

Causes of increasing return:- Following factors lead to increasing returns to a factor-

i. Indivisibility of the factors - Increase in units of variable factor leads to better and fuller utilisation of fixed factor. This causes the production to increase at a rapid rate.

ii. Efficient utilisation of variable factor - When more units of variable factor are employed with fixed factor, then variable factor is utilised in more efficient way.

iii. Optimum combination of factors - In the beginning when quantities of a variable factors are applied to fixed factors, the system moves towards achievement of optimum combination of factors because then underutilised fixed factors (building, machine, land etc) are better and more fully used. Thus lead to increasing returns.

iv. Specialisation- With more use of labour, process based division of labour and specialisation becomes possible which increases efficiency and productivity.