In Volume 1, Book 8, Chapter 25, Tristram and La Beale Isoud find themselves imprisoned. In an instance of satire, a knight informs Tristram of an "old custom of this castle" to which they will be subjected:
‘Sir,’ said the knight, ‘this is the old custom of this castle, that when a knight cometh here he must needs fight with our lord, and he that is the weaker must lose his head. And when that is done, if his lady that he bringeth be fouler than our lord’s wife, she must lose her head, and if she be fairer proved than is our lady, then shall the lady of this castle lose her head.’
‘So God help me,’ said Sir Tristram, ‘this is a foul custom and a shameful.[']
The knight tells Tristram here that he will have to fight with the lord of the castle, and whoever loses will be beheaded. What's more, La Beale Isoud's beauty will be compared to the beauty of the lord's wife: whoever is uglier will also be beheaded. All of this is going to happen in the name of "custom." Tristram is quick to criticize the custom as "foul" and "shameful." What he doesn't say is how ridiculous the custom is. What with one person in each couple being beheaded, the lord and lady of the castle are bound to change all the time. Not only that, but also they may end up swapping partners if one man and one woman from each couple are beheaded. Clearly, there is no logic or even a single person's thought process behind this rule, if the person in charge is constantly changing but doing nothing about the rule. The preposterous idea that this is how a society should be run satirizes the general idea of implementing rules based on "custom" or tradition. Just because something has always been done a certain way does not mean it is a good idea.
Malory was writing in the midst of the Wars of the Roses, a series of civil wars in England over which noble family would take the crown. Malory himself is believed to have switched sides multiple times depending on his own convenience, and later in life he committed a number of crimes, from assassination to sexual assault to financial crimes. (In fact, he wrote Le Morte d'Arthur from prison). He does not seem to have had much patience for rules he did not like or that did not make sense to him. He also does not seem to have had much patience for a civil war that no one would stop fighting. The silly custom at the castle where Tristram and La Beale Isoud are imprisoned stands in satirically for the whole set of "silly customs" Malory did not like in 15th-century England. This moment in the book satirizes not only the uncritical practice of traditions in Arthur's day, but also in Malory's day.
