One must submit to a of private liberty in order that one may enjoy a social order, which makes one's liberty a .
The sentence says accepting a limit on private freedom is what allows a workable society, and that trade makes freedom genuinely usable. The first blank needs a word meaning a restriction, and the second a word meaning something real. "Curtailment ... reality" captures both.
curtailment ... reality is the answer.
If the price of a commodity increases by 25%, by what percentage should the consumption be reduced to keep the expenditure the same?