Dirigible -- that's an airship, right?

“Precedent, n.
In Law, a previous decision, rule or practice which, in the absence of a definite statute, has whatever force and authority a Judge may choose to give it, thereby greatly simplifying his task of doing as he pleases.
As there are precedents for everything, he has only to ignore those that make against his interest and accentuate those in the line of his desire.
Invention of the precedent elevates the trial-at-law from the low estate of a fortuitous ordeal to the noble attitude of a dirigible (capable of being directed; steerable) arbitrament.”

(Look here for the Devil's Dictionary :
http://www.larkrise.co.uk/ddict.php?letter=P)

That last sentence seems to give a lot of people problems because it contains a couple of strange words used in rare ways. It could be rewritten to say:
"(The) invention of the Precedent aggrandizes a court trial from a difficult experience to find justice to a directable arbitration (of the prejudices of the judge or magistrate.)"

In other words, the guiding principle of Common Law, the eminent Precedent, only serves to allow the magistrate define 'Justice for All' any way he or she wishes on the day.