Thus in proposition I 1 it is assumed that circles with centers at the ends of a line segment and having the line segment as a common radius intersect .
And do not, somehow or, other, slip through each other with no common point.
Some sort of continuity postulate, such as one later furnished by R.
Dedekind, is needed to assure us of the existence of such a point of intersection .
Also, postulate P 1 guarantees the existence of at least one straight line joining two points A and B, but does not assure us that there cannot be more than one such joining line.