Axel Gelfert

The present paper focuses on a particular class of models intended to describe and explain the physical behaviour of systems that consist of a large number of interacting particles. Such many-body models are characterized by a specific Hamiltonian (energy operator) and are frequently employed in condensed matter physics in order to account for such phenomena as magnetism, superconductivity, and other phase transitions. Because of the dual role of many-body models as models of physical sys-tems (with specific physical phenomena as their explananda) as well as mathematical structures, they form an important sub-class of scientific models, from which one can expect to draw general conclusions about the function and functioning of models in science, as well as to gain specific insight into the challenge of modelling complex systems of correlated particles in condensed matter physics. In particular, it is argued that many-body models contribute novel elements to the process of inquiry and open up new avenues of cross-model confirmation and model-based understanding. In contradistinction to phenomenological models, which have received comparatively more philosophical attention, many-body models typically gain their strength not from ‘empirical fit’ per se, but from their being the result of a constructive application of mature formalisms, which frees them from the grip of both ‘fundamental theory’ and an overly narrow conception of ‘empirical success’.

In its original form due to Ian Hacking, entity realism postulates a criterion of manipulative success which replaces explanatory virtue as the criterion of justified scientific belief. The article analyses the foundations on which this postulate rests and identifies the conditions on which one can derive a form of entity realism from it. It then develops in detail an extensive class of counterexamples, drawing on the notion of quasi-particles in condensed matter physics. While the phenomena associated with quasi-particles pass the entity realist's criterion of manipulative success, quasi-particles themselves are illusions, and can be seen to be so even on the basis of the largely non-theoretical "home truths" that one must be ready to admit as background knowledge. Hence, Hacking's entity realism is shown to be incoherent.

Local reductionism purports to defend a middle ground in the debate about the epistemic status of testimony-based beliefs. It does so by acknowledging the practical ineliminability of testimony as a source of knowledge, while insisting that such an acknowledgment need not entail a default-acceptance view, according to which there exists an irreducible warrant for accepting testimony. The present paper argues that local reductionism is unsuccessful in its attempt to steer a middle path between reductionism and anti-reductionism about testimonial justification. In particular, it challenges local reductionism 'from within', without appealing to anti-reductionist intuitions. By offering novel arguments to the effect that local reductionism fails by its own standards, the present paper considerably strengthens the case against this version of reductionism. Local reductionism, it is argued, fails for three main reasons. First, it cannot account for the rationality of testimonial rejection in paradigmatic cases, even though the possibility of rational rejection is thought to be of central justificatory importance. Second, it does not provide a sufficiently distinct non-testimonial basis to which testimonial justification can be successfully reduced. Finally, local reductionism is shown to be an intrinsically unstable position, in danger of collapsing into full-fledged 'credulism' of the kind historically associated with Thomas Reid.

Inner speech is a pervasive feature of our conscious mental lives. Yet its function and character remain an issue of philosophical debate. The present paper focuses on the relation between inner speech and natural language and on the cognitive functions that various contributors have ascribed to inner speech. In particular, it is argued that inner speech does not consist of bare, context-free internal presentations of sentential (or subsentential) content, but rather has an ineliminably perspectival element. The proposed model of inner speech, which characterizes inner speech as akin to the testimony of an inner interlocutor, accounts for this perspectival element and, it is argued, is explanatorily superior, insofar as it better explains, amongst other phenomena, the often condensed character of inner speech.

Synthetic biology presents a challenge to traditional accounts of biology: Whereas traditional biology emphasizes the evolvability, variability, and heterogeneity of living organisms, synthetic biology envisions a future of homogeneous, humanly engineered biological systems that may be combined in modular fashion. The present paper approaches this challenge from the perspective of the epistemology of technoscience. In particular, it is argued that synthetic-biological artifacts lend themselves to an analysis in terms of what has been called ‘thing knowledge’. As such, they should neither be regarded as the simple outcome of applying theoretical knowledge and engineering principles to specific technological problems, nor should they be treated as mere sources of new evidence in the general pursuit of scientific understanding. Instead, synthetic-biological artifacts should be viewed as partly autonomous research objects which, qua their material-biological constitution, embody knowledge about the natural world—knowledge that, in turn, can be accessed via continuous experimental interrogation.