Lines Written in a Blank Page of Milton's Paradise Lost

This happy pair a certain bliss might prove,
Confin'd to constancy and mutual love:
Heaven to one object limited their vows,
The only safety faithless Nature knows.
God saw the wand'ring appetite would range,
And would have kept them from the pow'r to change;
But falsehood, soon as man increas'd, began;
Down through the race the swift contagion ran,
All ranks are tainted, all deceitful prove,
False in all shapes, but doubly false in love.
This makes the censure of the world more just,
That damns with shame the weakness of a trust!
Ere change began, our sex no scandal knew,
All nymphs were chaste as long as swains were true;
But now, tho' by the subtlest art betray'd,
We're so by custom and false maxims sway'd
That infamy still brands the injur'd maid.