"Love makes an ugly and rude person shine with beauty. It knows how to endow even one of humble birth with nobility, and it can lend humility to the proud." — Andreas Capellanus.
In the 12th century, Marie de Champagne, daughter of King Louis VII of France and Eleanor of Aquitaine, asked Andreas Cappellanus to write a De Amore, a text on courtly love. His three-book treatise included a definition of love and a list of rules for lovers that he said were an expansion of a list from King Arthur's court:
What is love?
Love is a certain inborn suffering derived from the sight of and excessive meditation upon the beauty of the opposite sex, which causes each one to wish above all things the embraces of the other and to carry out all of love's precepts in the other's embrace by common desire....
The Rules of Love
I. Marriage is no real excuse for not loving.
II. Anyone who is not jealous cannot love.
III. No one can be bound by a double love.
IV. It is well known that love is always increasing or decreasing
V. That which a lover takes against the will of his beloved has no relish.
VI. Boys do not love until they arrive at the age of maturity.
VII. When one lover dies, a widowhood of two years is required of the survivor.
VIII. No one should be deprived of love without the very best of reasons.
IX. No one can love except when impelled by the persuasion of love.
X. Love is always a stranger in the home of avarice.
XI. It is not proper to love any woman whom one would be ashamed to seek to marry.
XII. A true lover does not desire to embrace in love anyone except his beloved.
XIII. When made public, love rarely endures.
XIV. The easy attainment of love makes it of little value; difficulty of attainment makes it prized.
XV. Every lover regularly turns pale in the presence of his beloved.
XVI. When a lover suddenly catches sight of his beloved, his heart palpitates.
XVII. A new love puts to flight an old one.
XVIII. Good character alone makes any man worthy of love.
XIX. If love diminishes, it quickly fails and rarely revives.
XX. A man in love is always apprehensive.
XXI. Real jealousy always increases the feeling of love.
XXII. Jealously, and therefore love, are increased when one suspects his beloved.
XXIII. He who is vexed by the thought of love, eats and sleeps very little.
XXIV. Every act of a lover ends in the thought of his beloved.
XXV. A true lover considers nothing good except what he thinks will please his beloved.
XXVI. Love can deny nothing to love.
XXVII. A lover can never have enough of the solaces of his beloved.
XXVIII. A slight presumption causes a lover to suspect his beloved.
XXIX. A man who is vexed by too much passion usually does not love.
XXX. A true lover is constantly and without intermission possessed by the thought of his beloved.
XXXI. Nothing forbids one woman being loved by two men or one man by two women.