Two things are striking about this medieval definition. The first is that it is very close to the modern conception of formal consequence one finds in Bolzano and Tarski3. The second is that although Buridan and the other fourteenth-century logicians state these distinctions with a great deal of precision, they say almost nothing about the point of the distinctions. Why are these distinctions d...

Derived varieties were invented by P. Cohn in [4]. Derived varieties of a given type were invented by the authors in [10]. In the paper we deal with the derived variety Vσ of a given variety, by a fixed hypersubstitution σ. We introduce the notion of the dimension of a variety as the cardinality κ of the set of all proper derived varieties of V included in V. We examine dimensions of some varie...