The most devastating objection against Spinoza's thesis that there is only one substance in the universe is that raised by his contemporary Simon De Vries: If substance has an infinite number of distinct essences and substance is identical to its essence, how can there be only one substance?

The majority of Spinoza scholars have considered De Vries’ objection an insoluble problem. Joachim, for example, has stated:

In a paper entitled ‘Reviving the Logical Connection Argument,’ James Otten attempts to revive the Logical Connection Argument (LCA), which is intended to refute the causal thesis. Otten distinguishes two versions of the causal thesis. The general causal thesis:

(G) W1 … Wn are certain of S's wants, and W1 … Wn cause A,

and the restricted causal thesis:

(R): W is S's want to perform A, and W causes A.

In Chapter 5 of his book, Res Cogitans (1972), Zeno Vendler argued for the thesis that what we know when we know that p, e.g. that Los Angeles is south of San Francisco, and what we believe when we believe that p cannot be the same despite being expressed in the same words, on the ground that ‘believe’ is what he called a subjective verb and ‘know’ what he called an objective verb. For this he gave two main criteria (1) that subjective verbs can take only ‘subjective that- clauses,’ by which he means clauses which express propositions, whereas objective verbs can take only ‘objective that-clauses,’ by which he means clauses which express facts; (2) that subjective verbs cannot take, whereas objective verbs can take, wh- nominalisations - in practice these are the interrogatives what, who where, when, how - which Vendler also takes as a mark of the objective.

Richard Feldman in ‘Actions and De Re Beliefs’ attacks ‘latitudinarian’ accounts of de re belief in terms of de dicta belief, including those defended in print by one or the other of us. Feldman's case against latitudinarian views rests on the claim that such accounts do not allow de re attitudes an explanatory role they obviously can fulfil.

It is commonly said that ethical disputes either involve disagreements of fact or disagreements of principle and that while disagreements of fact can be overcome by rational means, disagreements of principle cannot. The difficulty is supposed to be this: for an argument to be rationally persuasive it must appeal to premises already accepted by the person to be persuaded, and if the premises include the principle in question then they will not be acceptable to that person; however, if the premises do not include the principle in question the argument cannot succeed because the conclusion can only validly be inferred from premises which do include the principle in question. While this doctrine is appealing to philosophers who find the idea of ultimate disagreement in ethics comforting, it is a visciously skeptical view which can be generalized to cover all systematic areas of human knowledge. As ‘disagreements of principle’ can appear in almost any domain of human inquiry, the hidden cost of this doctrine is terribly high.