This contribution defends two claims. The first is about why thought experiments are so relevant and powerful in mathematics. Heuristics and proof are not strictly and, therefore, the relevance of thought experiments is not contained to heuristics. The main argument is based on a semiotic analysis of how mathematics works with signs. Seen in this way, formal symbols do not eliminate thought experiments (replacing them by something rigorous), but rather provide a new stage for them. The formal world resembles the empirical world in that it calls for exploration and offers surprises. This presents a major reason why thought experiments occur both in empirical sciences and in mathematics. The second claim is about a looming aporia that signals the limitation of thought experiments. This aporia arises when mathematical arguments cease to be fully accessible, thus violating a precondition for experimenting in thought. The contribution focuses on the work of Vladimir Voevodsky (1966–2017, Fields medalist in 2002) who argued that even very pure branches of mathematics cannot avoid inaccessibility of proof. Furthermore, he suggested that computer verification is a feasible path forward, but only if proof is not modeled in terms of formal logic.

There are long-standing questions about the Big Bang: What were its properties? Was there nothing before it? Was the universe always here? Many conceptual issues revolve around time. This paper gives a novel model based on McTaggart’s temporal distinction between the A-series (future-present-past) and B-series (earlier-times to later-times). These series are useful while situated in a Presentist and Fragmentalist account of quantum mechanics, one in which the consistency with the Special Relativity (in particular the relativity of simultaneity) will be made explicit (section 6). This allows us to make a fruitful distinction between two pertinent questions: what happens as we go to earlier times toward the Big Bang? And: what happens as we go further into the past toward the Big Bang?

If we take the indexical, “I”, to be epistemologically identical across different contexts, as in, for example, it is the same “I” that at one moment observes, “I see a puddle of water on the floor”, and then, subsequently, exclaims, “I detect a leaking tap”, and, furthermore, we attribute not only self reference but self awareness in the use of the indexical, “I”, then a question arises as to how the “I” finds itself to be in reference to the speaker in one context and not another. We cannot look to the ingredients of the context that the “I” inhabits for the answer because, based upon the above assumptions, the identity, or character, of the “I” stands independently of the context of the speaker. The answer, I argue, requires both the admission of the unreality of space and time, as well as an explanation as to why we have a sense of the here and now despite space and time being unreal. To this end, I turn to the juxtaposition of Kant’s a priori forms of inner sense and outer sense to explain how the cognitive faculty arrives at a sense of time and place despite the declared unreality of time and space. To sustain this explanation in the face of the problem of localisation, I draw on the full implications of Kant’s transcendental idealism in which the properties of time and space are not only withdrawn from things as they exist externally to the mind but also from mental representations insofar as mental representations can be said to exist in themselves.

Inspired by Bermúdez's notion of proto-logic, I would like to fathom what the true proto-logic could be like. But this will be approached only in a negative way of figuring out what it could not be. I shall argue that it could not be purely deductive by exploiting the recent research in the logic of maps. This will allow us to reorient the search for proto-logic, starting with animal abduction. I will also suggest that proto-logic won't get off the ground without proto-geometry. These negative results will shed some light on some further conceptual and historical issues around the language of thought hypothesis to arrive at the true proto-logic.

The frame concept from linguistics, cognitive science and artificial intelligence is a theoretical tool to model how explicitly given information is combined with expectations deriving from background knowledge. In this paper, we show how the frame concept can be fruitfully applied to analyze the notion of mathematical understanding. Our analysis additionally integrates insights from the hermeneutic tradition of philosophy as well as Schmid’s ideal genetic model of narrative constitution. We illustrate the practical applicability of our theoretical analysis through a case study on extremal proofs. Based on this case study, we compare our analysis of proof understanding to Avigad’s ability-based analysis of proof understanding.

The notion of indivisibles and atoms arose in ancient Greece. The continuum—that is, the collection of points in a straight line segment, appeared to have paradoxical properties, arising from the ‘indivisibles’ that remain after a process of division has been carried out throughout the continuum. In the seventeenth century, Italian mathematicians were using new methods involving the notion of indivisibles, and the paradoxes of the continuum appeared in a new context. This cast doubt on the validity of the methods and the reliability of mathematical knowledge which had been regarded as established by the axiomatic method in geometry expounded by Aristotle’s younger contemporary Euclid. The teaching of indivisibles was banned within the Society of Jesus, the Jesuits. In England, indivisibles were used by the mathematician John Wallis, and there was an acrimonious and extended feud between Wallis and the philosopher Thomas Hobbes over legitimate methods of argument in mathematics. Notions of the infinitesimal were used by Isaac Newton and Gottfried Leibniz, and were attacked by Bishop Berkeley for the vagueness of the concept and the illegitimate reasoning applied to it. This article discusses aspects of these events with reference to the book Infinitesimal by Amir Alexander and to other sources. Also discussed are wider issues arising from Alexander’s book including: the changes in cultural sensibility associated with the growth of new mathematical and scientific knowledge in the seventeenth century, the changes in language concomitant with these changes, what constitutes valid methods of enquiry in various contexts, and the question of authoritarianism in knowledge. More general aims of this article are to widen the immediate mathematical and historical contexts in Alexander’s book, to bridge a gap in conversations between mathematics and the humanities, and to relate mathematical ideas to wider human and contemporary issues.