Rule of Construction is a rule used for interpreting legal instruments, especially contracts and statutes. Very few states have codified the rules of construction. Most states treat the rules as mere customs not having the force of law.
Contra proferentem and ejusdem generic are two examples of rules of construction. According to Contra proferentem rule, if a clause in a contract appears to be ambiguous, it should be interpreted against the interests of the person who insisted that the clause be included. Likewise ejusdem generis rule states that where a law lists specific classes of persons or things and then refers to them in general, the general statements only apply to the same kind of persons or things specifically listed.