The effect on the remainder of a statute when certain parts of it are held to be unconstitutional depends on whether the Legislature intended it to be severable. Severability is a contractual concept which permits a contract to survive despite an illegal or unenforceable provision within the contract. The illegal or unenforceable provision is excised from the contract and the contract is allowed to stand without it.
Severability also applies to statutes and regulations. And the question often is whether the courts have the authority to sever an unconstitutional portion of a statute or regulation, and enforce the rest.
For clarity sake, legislatures often insert a severability clause into its legislation and regulations. A typical severability clause is a stereotyped statement to the effect that if any provision is held unconstitutional the validity of the remainder shall be unaffected. This kind of statement, though not conclusive, is persuasive evidence of legislative intention. (Bacon Service Corp. v. Huss (1926) 199 C. 21, 34.) If so, the objectionable portions are void, but the rest of the statute remains valid. (See, e.g., Hale v. McGettigan (1896) 114 Cal. 112, 119.)
Where, however, to sustain the remaining valid portion would accomplish a result different from that intended by the Legislature or the People, the whole will be declared invalid. (Robert v. Police Court of San Francisco (1905) 148 C. 131.) Where the general provisions of a statute are constitutional but it contains an unconstitutional exception, the tendency is to sustain the statute and invalidate only the exception, particularly where there is a severability clause. (See Bacon Service Corp. v. Huss(1926) 199 C. 21, 32.)
A broader severability clause, now in more common use, contains language similar to the following: “If any provision of this act or the application thereof to any person or circumstances is held invalid, such invalidity shall not affect other provisions or applications of the act that can be given effect without the invalid provision or application, and to this end the provisions of this act are severable.” This kind of clause provides for what might be called “application severability”; the court is required to determine, not the validity of particular parts of the statute, but the validity of its application to particular persons under particular circumstances.
However, whether the court can engage in “application severability” to ultimately construe a law contrary to the express legislative intent at the time of enactment, to salvage what can be saved of the legislative purpose of the statute. In Metromedia v. San Diego ((1982) 32 Cal.3d 180), the Court held that a municipal billboard regulation unconstitutional on the ground that its prohibition on noncommercial billboards violated the First Amendment. The case was then remanded to the California court to determine whether constitutionality could be saved by construction, i.e., by limiting its scope to prohibit only commercial signs.
The court held that this construction would not be proper. It would be inconsistent with the language and original intent of the ordinance. It would leave the city with one less effective in achieving the city’s goals; and it would invite constitutional difficulties in distinguishing between commercial and noncommercial signs. (See Id. at 191.)

Two justices dissented, asserting that the “courts are fully authorized to undertake precisely this kind of constitutionally compelled editing and interpreting in order to uphold a legislative scheme insofar as it is constitutionally permissible”. (See Id. at 195.)