Another reason, which makes it necessary that this construction should be placed upon the word "_importation_," is, that the clause contains no other word that describes the immigration of foreigners. Yet that the clause related to the immigration of foreigners _generally_, and that it restrained congress, (up to the year 1808,) from prohibiting the immigration of foreigners generally, there can be no doubt. The object, and the only _legal_ object, of the clause was to restrain congress from so exercising their "power of regulating commerce with foreign nations, and among the several states, and with the Indian tribes"--(which power has been decided by the supreme court of the United States, to include a power over navigation and the transportation of passengers in boats and vessels[21])--as to obstruct the introduction of new population into such of the states as were desirous of increasing their population in that manner. The clause does not imply at all, that the population, which the states were thus to "admit," was to be a slave population. The word "importation," (I repeat,) is the only word in the clause, that applies to persons that were to _come into_ the country from foreign nations. The word "_migration_" applies only to those who were to _go out from_ one of our own states or territories into another. "_Migration_" is the act of _going out_ from a state or country; and differs from immigration in this, that immigration is the act of _coming into_ a state or country. It is obvious, therefore, that the "_migration_," which congress are here forbidden to prohibit, is simply the _going out_ of persons from one of our own states or territories into another--(for that is the only "_migration_" that could come within the jurisdiction of congress)--and that it has no reference to persons _coming in_ from foreign countries to our own. If, then, "migration," as here used, has reference only to persons _going out_ from one state into another, the word "_importation_" is the only one in the clause that is applicable to foreigners coming into our country. This word "importation," then, being the only word that can apply to persons coming into the country, it must be considered as substantially synonymous with immigration, and must apply equally to _all_ "persons," that are "imported," or brought into the country as passengers. And if it applies equally to all persons, that are brought in as passengers, it does not _imply_ that any of those persons are slaves; for no one will pretend that this clause ever authorized the state governments to treat as slaves _all_ persons that were brought into the country as passengers. And if it did not authorize them to treat all such passengers as slaves, it did not authorize them to treat any of them as such; for it makes no discrimination between the different "persons" that should be thus imported.