"[In the United States] the powers of the legislature are defined and
limited; and that those limits may not be mistaken, or forgotten, the
Constitution is written. To what purpose are powers limited, and to what
purpose is that limitation committed in writing if these limits may, at
any time, be passed by those intended to be restrained? The distinction
between a government with limited and unlimited powers is abolished, if
those limits do not confine the persons on which they are imposed, and
if acts prohibited and acts allowed are of equal obligation. It is a
proposition too plain to be contested: that the Constitution controls
any legislative act repugnant to it; or, that the legislature may alter
the Constitution by an ordinary act.

"[If, then,] an act of the legislature, repugnant to the Constitution,
is void, does it, notwithstanding its invalidity, bind the courts, and
oblige them to give it effect? Or, in other words, though it be not law,
does it constitute a rule as operative as if it was a law? This would be
to overthrow in fact what was established in theory; and would seem, at
first view, an absurdity too gross to be insisted on. It shall, however,
receive a more attentive consideration.

"It is emphatically the province and duty of the judicial department to
say what the law is. Those who apply the rule to particular cases, must
of necessity expound and interpret that rule. If two laws conflict with
each other, the courts must decide on the operation of each. So if a
law be in opposition to the Constitution; if both the law and the
Constitution apply to a particular case, so that the court must either
decide that case conformably to the law, disregarding the Constitution,
or conformably to the Constitution, disregarding the law, the court must
determine which of these conflicting rules governs the case. This is of
the very essence of judicial duty.

"[However, there are those who maintain] that courts must close their
eyes on the Constitution, and see only the law.... This doctrine would
subvert the very foundation of all written constitutions. It would
declare that an act which, according to the principles and theory of
our government, is entirely void, is yet, in practice, completely
obligatory. It would declare that if the legislature shall do what is
expressly forbidden, such act, notwithstanding the express prohibition,
is in reality effectual.

"[Moreover,] the peculiar expressions of the Cons