William of Ockham
Short Discourse on Tyrannical Government
Stanford Encyclopedia of Philosophy
Plurality is never to be posited without necessity.
Quaestiones et decisiones in quattuor libros Sententiarum Petri Lombardi
It is pointless to do with more what can be done with fewer.
Summa Totius Logicae
Logic is the most useful tool of all the arts. Without it no science can be fully known.