  Ockham did not allow any demonstration from final causes on the pattern of Grosseteste's demonstration of a material from a formal definition of an attribute, because he did not think that final causes have any genuine productive power. When a final cause is identified, the causal power involved is always the efficient causal power of some agent with a purpose in mind. This raised a problem with the account of the science of demonstration Ockham inherited from Grosseteste. Grosseteste expected the science of demonstration to argue from the function of demonstration to the material structure required to realize that function. The procedure seems inadmissible to Ockham, since it does not follow the path of actual (efficient) causation. Thus the demonstrations making up the science of demonstration seem to be illegitimate. Ockham responds to this problem by holding on to the formal structure that Grosseteste had identified for the science of demonstration, but making demonstration follow the natural (and reliably functional) efficient causal path from knowledge of its premisses to knowledge of its conclusion. Thus the conclusion that a demonstration has necessary premisses cannot be drawn concerning demonstration defined in terms of its purpose, but only for demonstration defined in such a way that that sort of thing actually produces knowledge. So the definition will be “a syllogism with necessary premisses etc,” which, as it happens, supposits for the same things as “syllogism intended by the artisan, the logician, to produce knowledge.” It is as though we were to define an axe by describing those aspects of its structure responsible for its functionality (a handle of a certain shape, a head made of iron with a sharp edge, etc.), and then deducing from this structure that it will actually serve that function (actually cut wood) under the right conditions, and then applying this piece of natural science to the practical issue by giving the advice to use an axe so defined in the appropriate way when one wants to cut wood.