Opening an extraordinary synod of nearly 200 senior clerics, Francis suggested the Church must address the present gulf between what it currently says on these issues and what tens of millions of believers actually do.
Thorny theological questions such as whether divorced and remarried believers should be able to receive communion will dominate two weeks of closed-door discussions set to pit conservative clerics against reformists led by German cardinal Walter Kasper.
Vatican insiders say Kasper has the backing of Francis but that the pontiff wants consensus for any change.
That stance was reflected in the sermon the pontiff delivered at the synod's opening mass.
In it, he urged bishops to be generous in understanding the problems faced by ordinary believers trying to live within the rules of the church.