Rigid, rigorous, strict, stringent are often used interchangeably in the sense of extremely severe and stern, especially when applied to laws or imposed conditions or to the persons who enforce them.
There are, however, differences in implications and in range of application. Basically rigid and rigorous imply extreme stiffness or utter lack of elasticity or flexibility, while strict and stringent imply tightness so extreme as to permit no looseness, laxity, or latitude.
These implications are preserved in their extended uses.
Rigid (see also STIFF ) in extended use is applied less often to persons than to their acts or to the conditions the persons make for themselves or others; it usually suggests uncompromising inflexibility.
Rigorous is applied to persons, to their acts, to their way of life, and to the natural or artificial conditions under which they live.
It commonly implies imposed severities or hardships; thus, a rigid rule admits of no change or compromise, but a rigorous rule imposes exacting or harsh conditions; a rigorous enforcement of a law makes the people feel its rigors; a rigid enforcement of a law admits of no relaxations in anyone’s favor; one can speak of a rigorous winter, a rigorous disciplinarian, the rigorous life of an explorer or a monk.
Strict is applied chiefly to persons or their acts and denotes showing or demanding undeviating conformity to rules, standards, conditions, or requirements; thus, a strict rule demands obedience; a strict teacher may impose rigorous discipline and adhere to a rigid system of grading; a strict watch admits no relaxing of vigilance, and strict silence no freedom to speak; a strict construction of a law is one confined to the letter of that law.
Stringent is to strict as rigorous is to rigid, in that it usually emphasizes the effect or effects rather than the presence of a quality in an agent or his act.
Both stringent and rigorous connote imposition, but stringent suggests impositions that limit, curb, or sometimes coerce; thus, a stringent rule narrows one’s freedom or range of activities; a stringent interpretation of the constitution may either be narrower or more restrictive in its effects than the letter of the constitution warrants; poverty may be described as stringent when it narrows one’s opportunities to satisfy one’s aspirations; necessity may be called stringent when it forces one to live within bounds or forces one into distasteful acts.