Example : Social relations impose courtesy.
Duty constrains one to act often contrary to one's desires or inclinations.

Synonyms : enforce, impose

Example : This holds the local until the express passengers change trains.
About a dozen animals were held inside the stockade.
The illegal immigrants were held at a detention center.
The terrorists held the journalists for ransom.

Synonyms : confine, hold, restrain

Example : Tighten the rules.
Stiffen the regulations.

Synonyms : stiffen, tighten, tighten up