A crucial part of the contemporary interest in logicism in the philosophy of mathematics resides in its idea that arithmetical knowledge may be based on logical knowledge. Here an implementation of this idea is considered that holds that knowledge of arithmetical principles may be based on two things: (i) knowledge of logical principles and (ii) knowledge that the arithmetical principles are representable in the logical principles. The notions of representation considered here are related to theory-based and structure-based notions of representation (...) from contemporary mathematical logic. It is argued that the theory-based versions of such logicism are either too liberal (the plethora problem) or are committed to intuitively incorrect closure conditions (the consistency problem). Structure-based versions must on the other hand respond to a charge of begging the question (the circularity problem) or explain how one may have a knowledge of structure in advance of a knowledge of axioms (the signature problem). This discussion is significant because it gives us a better idea of what a notion of representation must look like if it is to aid in realizing some of the traditional epistemic aims of logicism in the philosophy of mathematics. (shrink)

The thesis of quantifier variance is consistent and cannot be refuted via a collapse argument.

After proving, in a purely categorial way, that the inclusion functor $\textrm {In}_{\textbf {Alg}(\varSigma )}$ from $\textbf {Alg}(\varSigma )$, the category of many-sorted $\varSigma $-algebras, to $\textbf {PAlg}(\varSigma )$, the category of many-sorted partial $\varSigma $-algebras, has a left adjoint $\textbf {F}_{\varSigma }$, the (absolutely) free completion functor, we recall, in connection with the functor $\textbf {F}_{\varSigma }$, the generalized recursion theorem of Schmidt, which we will also call the Schmidt construction. Next, we define a category $\textbf {Cmpl}(\varSigma )$, of (...) $\varSigma $-completions, and prove that $\textbf {F}_{\varSigma }$, labelled with its domain category and the unit of the adjunction of which it is a part, is a weakly initial object in it. Following this, we associate to an ordered pair $(\boldsymbol {\alpha },f)$, where $\boldsymbol {\alpha }=(K,\gamma,\alpha )$ is a morphism of $\varSigma $-completions from ${{\mathscr {F}}}=(\textbf {C},F,\eta )$ to $\mathscr {G}= (\textbf {D},G,\rho )$ and $f$ a homomorphism of $\textbf {D}$ from the partial $\varSigma $-algebra $\textbf {A}$ to the partial $\varSigma $-algebra $\textbf {B}$, a homomorphism $\varUpsilon ^{\mathscr {G},0}_{\boldsymbol {\alpha }}(f)\colon \textbf {Sch}_{\boldsymbol {\alpha }}(f)\longrightarrow \textbf {B}$. We then prove that there exists an endofunctor, $\varUpsilon ^{\mathscr {G},0}_{\boldsymbol {\alpha }}$, of $\textbf {Mor}_{\textrm {tw}}(\textbf {D})$, the twisted morphism category of $\textbf {D}$, thus showing the naturalness of the previous construction. Afterwards, we prove that, for every $\varSigma $-completion $\mathscr {G}=(\textbf {D},G,\rho )$, there exists a functor $\varUpsilon ^{\mathscr {G}}$ from the comma category $(\textbf {Cmpl}(\varSigma )\!\downarrow \!\mathscr {G})$ to $\textbf {End}(\textbf {Mor}_{\textrm {tw}}(\textbf {D}))$, the category of endofunctors of $\textbf {Mor}_{\textrm {tw}}(\textbf {D})$, such that $\varUpsilon ^{\mathscr {G},0}$, the object mapping of $\varUpsilon ^{\mathscr {G}}$, sends a morphism of $\varSigma $-completion of $\textbf {Cmpl}(\varSigma )$ with codomain $\mathscr {G}$, to the endofunctor $\varUpsilon ^{\mathscr {G},0}_{\boldsymbol {\alpha }}$. (shrink)