With the weight of either of these considerations, when presented to Congress to influence its action, this court has no concern. One or the other may be justly entitled to guide or control the legislative judgment upon what is a needful regulation. The question here is, whether they are sufficient to authorize this court to insert into this clause of the Constitution an exception of the exclusion or allowance of slavery, not found therein, nor in any other part of that instrument. To engraft on any instrument a substantive exception not found in it, must be admitted to be a matter attended with great difficulty. And the difficulty increases with the importance of the instrument, and the magnitude and complexity of the interests involved in its construction. To allow this to be done with the Constitution, upon reasons purely political, renders its judicial interpretation impossible--because judicial tribunals, as such, cannot decide upon political considerations. Political reasons have not the requisite certainty to afford rules of juridical interpretation. They are different in different men. They are different in the same men at different times. And when a strict interpretation of the Constitution, according to the fixed rules which govern the interpretation of laws, is abandoned, and the theoretical opinions of individuals are allowed to control its meaning, we have no longer a Constitution; we are under the government of individual men, who for the time being have power to declare what the Constitution is, according to their own views of what it ought to mean. When such a method of interpretation of the Constitution obtains, in place of a republican Government, with limited and defined powers, we have a Government which is merely an exponent of the will of Congress; or what, in my opinion, would not be preferable, an exponent of the individual political opinions of the members of this court. If it can be shown, by anything in the Constitution itself, that when it confers on Congress the power to make _all_ needful rules and regulations respecting the territory belonging to the United States, the exclusion or the allowance of slavery was excepted; or if anything in the history of this provision tends to show that such an exception was intended by those who framed and adopted the Constitution to be introduced into it, I hold it to be my duty carefully to consider, and to allow just weight to such considerations in interpreting the positive text of the Constitution. But where the Constitution has said _all_ needful rules and regulations, I must find something more than theoretical reasoning to induce me to say it did not mean all. There have been eminent instances in this court closely analogous to this one, in which such an attempt to introduce an exception, not found in the Constitution itself, has failed of success.