Lawyers deal with the law every day, but seldom pause to ask the existential question - What is law?   Conveniently, the California legislature has provided some definitions.  Section 22 of the Civil Code defines "law" in decidedly magisterial terms:

"Law is a solemn expression of the will of the supreme power of the State."

How is that the supreme power express its will?  The answer can be found in Section 22.1 of the Civil Code which declaims that the "will of the supreme power is expressed" by the Constitution and statutes.   Notably absent is any mention of the judicial precedents.

Section 160 of the Evidence Code provides a broader and seemingly open-ended definition:

"'Law' includes constitutional, statutory, and decisional law."

Health & Safety Code Section 113816 takes the approach that law is law only if it is applicable, but omits the constitution and judicial precedent:

"'Law' means applicable local, state, and federal statutes, regulations, and ordinances."

The great Roman lawyer, Marcus Tullius Cicero, answers the question by quoting the learned men of his time as defining law as "Lex est ratio summa, insita in natura, quae iubet ea quae facienda sunt, prohibetque contraria (Law is the highest reason, ingrafted in nature, which commands what must be done and prohibits the contrary)".   De Legibus 1:18.   Cicero also observed that ignorance of the law leads to more litigation than knowledge of the law ("Potius ignoratio iuris litigiosa est quam scienta").  Id.