Delivered on the occasion of the 2009 “Giulio Preti Prize”, this lecture examines and questions the contrast between the sense of intellectual crisis in the scientific world of the first decades of the 20th century and the absence of any such sense of crisis in current philosophy. Starting in the 19the century, we were confronted with changes in perspective that affected our relation to the universe we live in as well as to our own language and logic. Not only how we see ourselves but the tools by means of which we think about ourselves came into question. How would it be possible to rationally assess conceptual change that affects the very form of reasoning by which we assess

such changes? Such are the paradoxes to which philosophers and scientists, in the throes of crisis in the first half of the 20th century, tried to respond. Philosophers today may seemingly have overcome those aporias that vexed their recent predecessors, in denial of the existence of a crisis that should actually be a fecund source for reflection.

In recent papers Hans Halvorson has offered a critique of the semantic view of theories, showing that theories may be the same although the corresponding sets of models are different and, conversely, that theories may be different although the corresponding sets of models are the same. This critique will be assessed, first, as it pertains to issues concerning scientific models in the empirical sciences and, second, independent of any concern with empirical science.

A scientific theory offers models for the phenomena in its domain; these models involve theoretical quantities, and a model's structure is the set of relations it imposes on these quantities. A fundamental demand in scientific practice is for those quantities to be clearly and feasibly related to measurement. This demand for empirical grounding can be articulated by displaying the theory-dependent criteria for a procedure to count as a measurement and for identifying the quantity it measures.

There are a number of dimensions to the realism-nominalism controversy. The topics of debate comprise: necessary connections and causality, dispositions and counterfactuals, space and time, the existence of abstract entities and mathematical objects, the existence of the theoretical entities of science. On all these except the last, Sellars takes a non-realist line: and on all these except the last, I agree with him to the extent that I presently have an opinion on them. But Sellars is a scientific realist, encapsulating this realism in the dictum: “to have good reason for holding a theory is ipso facto to have good reason for holding that the entities postulated by the theory exist” ([2], p. 91).

There have recently appeared some studies in which Aristotle's views on science are related to modern philosophical issues and distinctions, some articles in which a return to at least some of his ideas is suggested as a solution to certain modern problems, and also some advocacy of the essentialism or modal realism that is historically associated with the Aristotelian tradition.

Personal probability is now a familiar subject in epistemology, together with such more venerable notions as knowledge and belief. But there are severe strains between probability and belief; if either is taken as the more basic, the other may suffer. After explaining the difficulties of attempts to accommodate both, I shall propose a unified account which takes conditional personal probability as basic. Full belief is therefore a defined, derivative notion. Yet we will still be able to picture opinion as follows: my subjective probability is only a grading of the possibilities left open by my beliefs. My conditional probabilities generally derive — in a sense to be explicated — from the strongest belief I can maintain when admitting the relevant condition.

Professor Roeper adresses a large question, whether probabilistic semantics is a kind of semantics at all. Happily, he does this via an exploration of a specific issue on which he and Professor Leblanc have done important work. That is the issue of how the relationship of logical consequence can be characterized as a relation denned in terms of probability. Let us follow him in calling a relevant relationship of the latter sort the degree of implication, and follow Professor Roeper on his quest for a satisfactory one.

What does it mean to embed the phenomena in an abstract structure? Or to represent them by doing so? The semantic view of theories runs into a severe problem if these notions are construed either naively, in a metaphysical way, or too closely on the pattern of the earlier syntactic view. Constructive empiricism and structural realism will then share those difficulties. The problem will be posed as in Reichenbach's The Theory of Relativity and A Priori Knowledge, and realist reactions will be examined, but they will be argued to dissolve upon scrutiny.

Criteria of adequacy for scientific representation of the phenomena pertain to accuracy and truth. But that representation is selective and may require distortion even in the selected parameters; this point is intimately connected with the fact that representation is intentional, and its adequacy relative to its particular purpose. Since observation and measurement are perspectival and the appearances to be saved are perspectival measurement outcomes, the question whether this “saving” is an explanatory relation provides a new focus for the realist/antirealist debate. The Born rule and von Neumann's “collapse” postulate in quantum mechanics provide a telling case for this question in recent physics.

Constructive empiricism is indeed set squarely within a common sense realism that was foreign to much of the empiricist tradition. But I do not see this common sense realism, which I take myself to share with many scientific realists, as harboring or leading to scientific realism. That is in part because of the way I separate the opposition between empiricist and realist understanding of science from other issues that divide us in epistemology. This discussion brought to light our quite different conceptions of what is at issue between empiricists and realists in this area. After a response to McMullin's critique, however, I will be especially concerned to respond to his challenging proposal for a shift in the debate over realism concerning the sciences.

A recent article (Leeds and Healey 1996) argues that the modal interpretation (Copenhagen variant) of quantum mechanics does not do justice to immediately repeated non-disturbing measurements. This objection has been raised before, but the article presents it in a new, detailed, precise form. I show that the objection is mistaken.

Feyerabend's “Classical Empiricism” (1970) draws on a 17th century Jesuit argument against Protestant fundamentalism. The argument is very general, and applies to any simple foundationalist epistemology. Feyerabend uses it against Classical Empiricism—roughly, the view that what is to be believed is exactly what experience establishes, and no more—which he identifies as among other things Newton's “dogmatic ideology.”

Traditionally, philosophy of science has focused on the product of science: the scientific hypothesis, principle, law, or more grandiosely, the theory. Using logician's license I'll think of hypotheses and theories as ‘little’ and ‘big’ (or ‘weak’ and ‘strong’) propositions. The tradition spoke of the product as (scientific) knowledge; the more recent phrase “current scientific opinion” carries the same connotation of uniqueness. For this to make sense, something is required: a proposition must be capable of being true or false, capable of being fully believed or disbelieved (and if you like, known).

Probabilism requires us to look at every aspect of science in a new way. In his radical brand of probabilism, Richard Jeffrey told us to reconceptualize knowledge as 'probable knowledge’ and propositions as ‘probasitions’—and never to resolve doubt but simply to quantify it, keeping all possibilities in play.