Gouverneur Morris was one of the few delegates at the Philadelphia Convention who spoke openly against domestic slavery.
According to James Madison, who took notes at the Convention, Morris spoke openly against slavery on 8 August 1787, saying that it was incongruous to say that a slave was both a man and property at the same time:
He [Morris] never would concur in upholding domestic slavery.
It was a nefarious institution.
It was the curse of heaven on the states where it prevailed.
Compare the free regions of the Middle States, where a rich & noble cultivation marks the prosperity & happiness of the people, with the misery & poverty which overspread the barren wastes of Va. Maryd. &
the other States having slaves. ...
Proceed southwardly, and every step you take, through the great regions of slaves, presents a desert increasing with the increasing proportion of these wretched beings.

Upon what principle is it that the slaves shall be computed in the representation?
Are they men?
Then make them citizens, and let them vote.
Are they property?
Why, then, is no other property included?
The Houses in this city [Philadelphia] are worth more than all the wretched slaves which cover the rice swamps of South Carolina.

According to Madison, Morris felt that the U.S. Constitution's purpose was to protect the rights of humanity and that to promote slavery was incongruous with it:
The admission of slaves into the Representation when fairly explained comes to this: that the inhabitant of Georgia and S. C. who goes to the Coast of Africa, and in defiance of the most sacred laws of humanity tears away his fellow creatures from their dearest connections & damns them to the most cruel bondages, shall have more votes in a Govt.
instituted for protection of the rights of mankind, than the Citizen of Pa. or N. Jersey who views with a laudable horror, so nefarious a practice.
Gouverneur Morris was one of the few delegates at the Philadelphia Convention who spoke openly against domestic slavery. According to James Madison, who took notes at the Convention, Morris spoke openly against slavery on 8 August 1787, saying that it was incongruous to say that a slave was both a man and property at the same time:
He [Morris] never would concur in upholding domestic slavery. It was a nefarious institution. It was the curse of heaven on the states where it prevailed. Compare the free regions of the Middle States, where a rich & noble cultivation marks the prosperity & happiness of the people, with the misery & poverty which overspread the barren wastes of Va. Maryd. & the other States having slaves. ... Proceed southwardly, and every step you take, through the great regions of slaves, presents a desert increasing with the increasing proportion of these wretched beings.
Upon what principle is it that the slaves shall be computed in the representation? Are they men? Then make them citizens, and let them vote. Are they property? Why, then, is no other property included? The Houses in this city [Philadelphia] are worth more than all the wretched slaves which cover the rice swamps of South Carolina.
According to Madison, Morris felt that the U.S. Constitution's purpose was to protect the rights of humanity and that to promote slavery was incongruous with it:
The admission of slaves into the Representation when fairly explained comes to this: that the inhabitant of Georgia and S. C. who goes to the Coast of Africa, and in defiance of the most sacred laws of humanity tears away his fellow creatures from their dearest connections & damns them to the most cruel bondages, shall have more votes in a Govt. instituted for protection of the rights of mankind, than the Citizen of Pa. or N. Jersey who views with a laudable horror, so nefarious a practice.
Gouverneur Morris