A wealth of possible meanings may be attached to James Madison’s cryptic statement, “... Where slavery exists, the Republican Theory becomes still more fallacious.” On the one hand, he may simply be referring to the fear that slaves may unite with white rebel factions, which would endanger the principle that rule should be by a majority of citizens. In Federalist No. 43 he warns that “in the tempestuous scenes of civil violence,” slaves may “give a superiority of strength to any party with which they may associate themselves.” If that is his meaning, then it is merely a pragmatic consideration, based on the widespread fear of slave uprisings, and not a statement of moral or political principle.
On the other hand, Madison also believed that the prevalence of slavery in the South invalidated some states’ claims to possessing a republican form of government. Within his private notes, Madison wrote that many Southern States, like many ancient regimes, were republican in name only. Their democratic pretensions were called into question partly because of the high property qualifications for suffrage in some of these states, but principally because of the number of slaves who were excluded from the political process. To be a genuinely republican form of government, according to Madison, a critical mass of adult male residents must be in possession of full political rights. If this is Madison’s meaning here, then this brief comment about the republican theory being “fallacious” in those states where slavery exists should be interpreted as an indictment of those state laws that permit slavery.