Perhaps the most obvious contradiction in the Constitution is the contradiction with regard to slavery.
In the Constitution, all Americans are given the right to various liberties. For example, the Fifth Amendment guarantees that "no person shall ... be deprived of life, liberty, or property, without due process of law." This idea is clearly contradicted by the existence of slavery. Every slave was deprived of his or her liberty by slavery. Many were deprived of life and none really had any right to property. Of course, slavery is not explicitly made legal in the Constitution, but it is implicitly accepted in such things as the fugitive slave clause and the three-fifths compromise. Thus, the Constitution conlicts with itself by both allowing slavery and guaranteeing personal liberty.