That which is contrary to the constitution. 2. When an act of the legislature is repugnant or contrary to the constitution, it is, ipso facto, void. 3. The courts have the power, and it is their duty, when an act is unconstitutional, to declare it to be so; but this will not be done except in a clear case and, as an additional guard against error, the supreme court of the United States refuses to take up a case involving constitutional questions, when the court is not full.