Q.Critically examine the Law of Variable Proportions.
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Start your 14-day free trial to unlock the full solution →The Law of Variable Proportions (the short-run law of production) says that when more and more units of a variable factor are combined with fixed factors, marginal product first rises (Stage I — increasing returns), then falls but stays positive (Stage II — diminishing returns), and finally becomes negative (Stage III — negative returns). A rational producer always operates in Stage II. Critically, the law holds because factors are imperfectly substitutable and fixed factors become over-/under-utilised, but it assumes constant technology, homogeneous variable units and a short period, so it does not apply where factors are used in rigidly fixed proportions or where technology changes.
Statement
When the quantity of one variable factor is increased while the quantities of other factors are held fixed, the total product increases first at an increasing rate, then at a diminishing rate, and finally decreases. This happens because the proportion between the fixed and variable factors keeps changing.
The Three Stages
Stage I — Increasing Returns: Total Product (TP) rises at an increasing rate and Marginal Product (MP) rises. The fixed factor is underutilised, so adding the variable factor improves the factor ratio and raises efficiency.
Stage II — Diminishing Returns: TP rises but at a diminishing rate; MP falls and remains positive; Average Product (AP) also falls. TP reaches its maximum at the end of this stage where MP = 0. A rational producer operates here because output is highest and still rising.
Stage III — Negative Returns: TP actually falls and MP becomes negative. Too much of the variable factor is crowded onto the fixed factor, lowering total output. No producer operates here.
Causes of the Law
- Fixity of factors — in the short run some factors cannot be varied.
- Imperfect substitutability of factors — variable factors cannot fully replace fixed ones.
- Optimum factor proportion — up to the optimum ratio returns increase; beyond it they diminish.
Critical Examination
Points in favour:
- It is realistic — it applies to agriculture, mining and most short-run production where some factor is fixed.
- It is a general law, confirmed by observation.
- It usefully guides the producer to Stage II.
Criticisms / Limitations:
- It applies only to the short run; in the long run all factors are variable (then the Laws of Returns to Scale apply). …
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