This impression is quite erroneous.

It was one of the details of the compromise, but it had been a feature of the revenue amendment of 1783, and it was generally accepted as a happy solution of the difficulty that slaves possessed the attributes both of persons and of property.

It had been included both in the amended Virginia Plan and in the New Jersey Plan; and when it was embodied in the compromise it was described as "the ratio recommended by Congress in their resolutions of April 18, 1783." A few months later, in explaining the matter to the Massachusetts convention, Rufus King said that, "This rule...

was adopted because it was the language of all America." In reality the three-fifths rule was a mere incident in that part of the great compromise which declared that "representation should be proportioned according to direct taxation." As a further indication of the attitude of the Convention upon this point, an amendment to have the blacks counted equally with the whites was voted down by eight States against two.
With the adoption of the great compromise a marked difference was noticeable in the attitude of the delegates.

Those from the large States were deeply disappointed at the result and they asked for an adjournment to give them time to consider what they should do.