A dummy set of advocates and knowledge accessors with knowledge about the death of Julius Caesar.

The Case Against Marcus Brutus

Did Brutus conspire to kill Caesar in the forum in the Ides of March?

Falco, the detective, must find out.

The witnesses

Anthony knows that Brutus is honourable, and that Caesar is buried.

Brutus will admit he was in the forum on the ides of March and is a witness that Cassius was also present.

Cassius and Longus each bear witness that the other killed Caesar in the Forum on the Ides of March.

Drusilla believes that Brutus killed Caesar in the Forum on the Ides of March, but was not a witness. She also bears witness that Caesar was buried on the 18th March.

Gaius believes that Brutus killed Caesar in the Forum in April, but was not a witness.

The rules

There is a rule which says that if you kill someone and you have accomplices then you’re not honourable, and a default that has-accomplices is false.

Note that has-accomplices boils down to

For a given verb, object, location and time, there is more than one subject.

That’s quite sophisticated to represent.

There is a rule which says you can’t be killed after you’re dead (temporal reasoning).

There is a rule which says if you’ve been killed or been buried then you’re dead.

The case against Brutus is based on Drusilla’s claim and on Gaius’s.

Drusilla’s can be doubted because 1. She wasn’t a witness and 2. Is a woman.

Gaius’s can be doubted because 1. he wasn’t a witness, and because 2. it’s inconsistent with the evidence that Caesar was buried on the 18th.

The conclusion

Thus, I think, Falco must conclude that Brutus didn’t kill Caesar, because if he had he must have had accomplices (Cassius and Longus, who clearly were accomplices and implicate one another), but honourable men don’t kill with accomplices and Brutus is an honourable man.

Features

The features in DTree terms we’re interested in to make these inferences are

• did-kill - true of an entity which is in the subject position of a kill proposition;
• was-killed - true of an entity which is in the object position of a kill proposition;
• buried - true of an entity which is in the object position of a bury proposition;
• dead - true of an entity of which either was-killed or buried is true;
• honourable - true of an entity, provided that did-lie and did-murder are false;
• did-murder - true of an entity x that did-kill[x,y] for some object y is true of, provided that there exists some other entity p of whom did-kill[p,x] is also true, or that was-unarmed[y] is true;
• did-lie - true of an entity which has offered a proposition which for other reasons we do not believe. Tricky. False by default and I think we probably leave it at that for now.
• was-unarmed - true of an entity at a time t if they were unarmed at the time.

Note that ALL of this is too complex for the simple DTree logic of the Arboretum / KnacqTools generation. They could not unpack propositions as I’m proposing here.