Psychometrics is one of the main approaches to social scientific measurement. It is relied upon in drug testing, economic policymaking, recruitment, and other decision-making contexts. The first aim of this article is to introduce philosophers to key aspects of psychometrics, namely, classical test theory, item response theory, and construct validity. The second aim is to show how a debate on the nature of psychological attributes manifests in psychometrics. In this debate, realists claim that psychometric measures are indicators of independently existing (...) qualities, while operationalists argue that a measure defines its target attribute. The third and final aim is to argue that despite its poor reputation among philosophers, operationalism is a viable approach to psychometrics. (shrink)

I review the philosophical literature on the question of when two physical theories are equivalent. This includes a discussion of empirical equivalence, which is often taken to be necessary, and sometimes taken to be sufficient, for theoretical equivalence; and “interpretational” equivalence, which is the idea that two theories are equivalent just in case they have the same interpretation. It also includes a discussion of several formal notions of equivalence that have been considered in the recent philosophical literature, including (generalized) definitional (...) equivalence and categorical equivalence. The article concludes with a brief discussion of the relationship between equivalence and duality. The article is in two parts; this is Part 2, which addresses categorical equivalence, interpretational equivalence, and duality. (shrink)

When discrepancies are discovered between the outcomes of different measurement procedures, two sorts of explanation are open to scientists. Either some of the outcomes are inaccurate or the procedures are not measuring the same quantity. I argue that, due to the possibility of systematic error, the choice between and is underdetermined in principle by any possible evidence. Consequently, foundationalist criteria of quantity individuation are either empty or circular. I propose a coherentist, model-based account of measurement that avoids the underdetermination problem, (...) and use this account to explain how scientists individuate quantities in practice. (shrink)

in april 1933, two bright young Ph.D.s were elected to the Harvard Society of Fellows: the psychologist B. F. Skinner and the philosopher/logician W. V. Quine. Both men would become among the most influential scholars of their time; Skinner leads the "Top 100 Most Eminent Psychologists of the 20th Century," whereas philosophers have selected Quine as the most important Anglophone philosopher after the Second World War.1 At the height of their fame, Skinner and Quine became "Edgar Pierce twins"; the latter (...) obtaining the endowed chair at Harvard's department of philosophy, the former taking up the position at Harvard's psychology department.2Besides these biographical parallels, there also... (shrink)

Presented here is an overview from the standpoints of sociology, history of science, philosophy of science and “pure science” of the lingering question of whether sociology is a form of scientific pursuit. The conclusion is drawn that sociology barely meets any of the rigid criteria traditionally associated with the natural sciences. Sociology is viewed as having a position of theory and argument which is labeled “inconoclastic scepticism.”.

Discussions of the relation between pragmatism and logical empiricism tend to focus on the period when the logical empiricists found themselves in exile, mostly in the United States, and then attempt to gauge the actual extent of their convergence. My concern lies with the period before that and the question whether pragmatism had an earlier influence on the development of logical empiricism, especially on the thought of the former members of the “first” Vienna Circle. I argue for a substantially qualified (...) affirmative answer. (shrink)

Scientific realists believe both what a scientific theory says about observables and unobservables. In contrast, scientific antirealists believe what a scientific theory says about observables, but not about unobservables. I argue that scientific realism is a more useful doctrine than scientific antirealism in science classrooms. If science teachers are antirealists, they are caught in Moore’s paradox when they help their students grasp the content of a scientific theory, and when they explain a phenomenon in terms of a scientific theory. Teachers (...) ask questions to their students to check whether they have grasped the content of a scientific theory. If the students are antirealists, they are also caught in Moore’s paradox when they respond positively to their teachers’ questions, and when they explain a phenomenon in terms of a scientific theory. Finally, neither teachers nor students can understand phenomena in terms of scientific theories, if they are antirealists. (shrink)

The current consensus view of causation in physics, as commonly held by scientists and philosophers, has several serious problems. It fails to provide an epistemology for the causal knowledge that it claims physics to possess; it is inapplicable in a prominent area of physics (classical thermodynamics); and it is difficult to reconcile with our everyday use of causal concepts and claims. In this dissertation, I use historical examples and philosophical arguments to show that the interventionist account of causation constitutes a (...) promising alternative for a “physically respectable” account of causation. The interventionist account explicates important parts of the experimental practice of physics and important aspects of the ways in which physical theory is used and applied. Moreover, the interventionist account succeeds where the consensus view of causation in physics fails. I argue that the interventionist account provides an epistemology of causal knowledge in physics that is rooted in experiment. On the interventionist view, there is a close link between experiment and the testing of causal claims. I give several examples of experiments from the early history of thermodynamics that scientists used in interventionist-type arguments. I also argue that interventionist claims made in the context of a physical theory can be epistemically justified by reference to the experimental interventions and observations that serve as evidence for the theory. I then show that the interventionist account of causation is well-suited to the patterns of reasoning that are intrinsic to thermodynamic theory. I argue that interventionist reasoning constitutes the structural foundation of thermodynamic theory, and that thermodynamic theory can provide clear answers to meaningful questions about whether or not a certain variable is a cause of another in a given context. Finally, I argue that the interventionist account offers the prospect of a unification of “physically respectable” causation and our everyday notion of causation. I conclude the dissertation by sketching an anti-foundationalist unification of causation, according to which causal reasoning occurs in the same manner in physics as it does in other branches of life and scientific research. (shrink)

El recurso cognitivo por el cual la ciencia ha obtenido información del mundo empírico ha sido, desde su origen, la medición. Ésta está sujeta a un proceso continuo de regeneración y transformación histórica. Los principales análisis metateóricos que se han realizado sobre la medición son en su mayoría sobre sus aspectos formales. En este artículo desarrollo un bosquejo de un enfoque histórico y cognitivo de la medición científica con el fin de mostrar sus diversos aspectos cognitivos, metodológicos y epistemológicos, mismos (...) que han sido sistemáticamente descuidados por la gran mayoría de los análisis en filosofía de la ciencia. Measurement has been the main cognitive resource through which science has obtained empirical information about the world. Scientific measurement is not a fixed process but an historical and dynamical one; nevertheless, almost all philosophical analysis have studied it from a formal point of view. My aim in this paper is to outline a cognitive and historical notion of scientific measurement that allows us to appreciate its diverse epistemic, methodological, and cognitive features. (shrink)

This paper is a supplement to, and provides a proof of principle of, Kuhn vs. Popper on Criticism and Dogmatism in Science: A Resolution at the Group Level. It illustrates how calculations may be performed in order to determine how the balance between different functions in science—such as imaginative, critical, and dogmatic—should be struck, with respect to confirmation (or corroboration) functions and rules of scientific method.

The last forty years have produced a dramatic reversal in leading accounts of science. Once thought necessary to (explain) scientific progress, a rigid method of science is now widely considered impossible. Study of products yields to study of processes and practices, .unity gives way to diversity, generality to particularity, logic to luck, and final justification to heuristic scaffolding. I sketch the story, from Bacon and Descartes to the present, of the decline and fall of traditional scientific method, conceived as The (...) Central Planning Bureau for Science or as Rationality Czar. I defend a deflationary account of method and of rational judgment,. with emphasis on heuristic appraisal and cognitive economy. (shrink)

This work develops an epistemology of measurement, that is, an account of the conditions under which measurement and standardization methods produce knowledge as well as the nature, scope, and limits of this knowledge. I focus on three questions: (i) how is it possible to tell whether an instrument measures the quantity it is intended to? (ii) what do claims to measurement accuracy amount to, and how might such claims be justified? (iii) when is disagreement among instruments a sign of error, (...) and when does it imply that instruments measure different quantities? Based on a series of case studies conducted in collaboration with the US National Institute of Standards and Technology (NIST), I argue for a model-based approach to the epistemology of physical measurement. To measure a physical quantity, I argue, is to estimate the value of a parameter in an idealized model of a physical process. Such estimation involves inference from the final state (‘indication’) of a process to the value range of a parameter (‘outcome’) in light of theoretical and statistical assumptions. Contrary to contemporary philosophical views, measurement outcomes cannot be obtained by mapping the structure of indications. Instead, measurement outcomes as well as claims to accuracy, error and quantity individuation can only be adjudicated relative to a choice of idealized modelling assumptions. (shrink)

In this paper I adduce a new argument in support of the claim that IBE is an autonomous form of inference, based on a familiar, yet surprisingly, under-discussed, problem for Hume’s theory of induction. I then use some insights thereby gleaned to argue for the claim that induction is really IBE, and draw some normative conclusions.

In the context of psychiatric diagnosis, operationists claim that mental disorders are nothing more than the satisfying of objective diagnostic criteria, whereas realists claim that mental disorders are latent entities that are detected by applying those criteria. The implications of this distinction are substantial in actual clinical situations, such as in the co-occurrence of disorders that may interfere with one another's detection, or when patients falsify their symptoms. Realist and operationist conceptions of diagnosis may lead to different clinical decisions in (...) these situations, affecting treatment efficacy and ultimate patient outcomes. (shrink)

The article discusses Friedman's classic claim that economics can be based on irrealistic assumptions. It exploits Samuelson's distinction between two "F-twists" (that is, "it is an advantage for an economic theory to use irrealistic assumptions" vs "the more irrealistic the assumptions, the better the economic theory"), as well as Nagel's distinction between three philosophy-of-science construals of the basic claim. On examination, only one of Nagel's construals seems promising enough. It involves the neo-positivistic distinction between theoretical and non-theoretical ("observable") terms; so (...) Friedman would in some sense argue for the major role of theoretical terms in economics. The paper uses a model-theoretic apparatus to refine the selected construal and check whether it can be made to support the claim. This inquiry leads to essentially negative results for both F-twists, and the final conclusion is that they are left unsupported. (shrink)

If a specific question has meaning, it must be possible to find operations by which an answer may be given to it. It will be found in many cases that the operations cannot exist, and the question therefore has no meaning. —Bridgman, The Logic of Modern Physics..

In October 1924, The Physical Review, a relatively minor journal at the time, published a remarkable two-part paper by John H. Van Vleck, working in virtual isolation at the University of Minnesota. Van Vleck used Bohr's correspondence principle and Einstein's quantum theory of radiation to find quantum formulae for the emission, absorption, and dispersion of radiation. The paper is similar but in many ways superior to the well-known paper by Kramers and Heisenberg published the following year that is widely credited (...) to have led directly to Heisenberg's Umdeutung paper. As such, it clearly shows how strongly the discovery of matrix mechanics depended on earlier work on the application of the correspondence principle to the interaction of matter and radiation. (shrink)

Niels Bohr famously argued that a consistent understanding of quantum mechanics requires a new epistemic framework, which he named complementarity . This position asserts that even in the context of quantum theory, classical concepts must be used to understand and communicate measurement results. The apparent conflict between certain classical descriptions is avoided by recognizing that their application now crucially depends on the measurement context. ;Recently it has been argued that a new form of complementarity can provide a solution to the (...) so-called information loss paradox. Stephen Hawking argues that the evolution of black holes cannot be described by standard unitary quantum evolution, because such evolution always preserves information, while the evaporation of a black hole will imply that any information that fell into it is irrevocably lost---hence a "paradox." Some researchers in quantum gravity have argued that this paradox can be resolved if one interprets certain seemingly incompatible descriptions of events around black holes as instead being complementary. ;In this dissertation I assess the extent to which this black hole complementarity can be undergirded by Bohr's account of the limitations of classical concepts. I begin by offering an interpretation of Bohr's complementarity and the role that it plays in his philosophy of quantum theory. After clarifying the nature of classical concepts, I offer an account of the limitations these concepts face, and argue that Bohr's appeal to disturbance is best understood as referring to these conceptual limits. ;Following preparatory chapters on issues in quantum field theory and black hole mechanics, I offer an analysis of the information loss paradox and various responses to it. I consider the three most prominent accounts of black hole complementarity and argue that they fail to offer sufficient justification for the proposed incompatibility between descriptions. ;The lesson that emerges from this dissertation is that we have as much to learn from the limitations facing our scientific descriptions as we do from the successes they enjoy. Because all of our scientific theories offer at best limited, effective accounts of the world, an important part of our interpretive efforts will be assessing the borders of these domains of description. (shrink)

This paper aims to reassess the philosophical puzzle of the “applicability of mathematics to physical sciences” as a misunderstood disciplinary interplay. If the border isolating mathematics from the empirical world is based on appropriate criteria, how does one explain the fruitfulness of its systematic crossings in recent centuries? An analysis of the evolution of the criteria used to separate mathematics from experimental sciences will shed some light on this question. In this respect, we will highlight the historical influence of three (...) major disciplinary paradigms. According to the Aristotelian classification of the sciences, the separation of mathematics from physics is based on their respective objects of study. The Baconian system distinguishes these sciences by the type of knowledge involved in each field. Finally, the Whewellian disciplinary layout categorises these disciplines by their respective methods. In this paper, we argue that the cascading effect of such disciplinary categorisations—based successively on ontological, epistemological, and heuristic criteria—resulted in a profound redefinition of the border between mathematics and physics, with the consequence of obscuring the foundations of the interplay between these fields. Our approach intends to put forward such a mechanism as a constitutive piece of the puzzle of the applicability of mathematics. (shrink)

The ArgumentThis paper explores the confrontation of physical and contextual factors involved in the emergence of the subject of color measurement, which stabilized in essentially its present form during the interwar period. The contentions surrounding the specialty had both a national and a disciplinary dimension. German dominance was curtailed by American and British contributions after World War I. Particularly in America, communities of physicists and psychologists had different commitments to divergent views of nature and human perception. They therefore had to (...) negotiate a compromise between their desire for a quantitative system of description and the perceived complexity and human-centeredness of color judgment. These debates were played out not in the laboratory but rather in institutionalized encounters on standards committees. Such groups constitute a relatively unexplored historiographic and social site of investigation. The heterogeneity of such committees, and their products, highlight the problems of identifying and following such ephemeral historical “actors”. (shrink)

A central difficulty in the way of understanding Spinoza's metaphysical system is that of reconciling two apparently contradictory theories of the causation of finite modes found in his Ethics. The easiest way to present the problem is to place these two accounts side by side.A. All things which follow from the absolute nature of any attribute of God must forever exist, and must be infinite; that is to say, through that attribute they are eternal and infinite. A thing which has (...) been determined to any action was necessarily so determined by God. Together, these propositions entail that God is a necessary and sufficient condition for the occurrence of any action, and that anything so determined is eternal and infinite. Compare these implications with the following.B. An individual thing or a thing which is finite and has determinate existence cannot exist nor be determined to action unless it be determined to existence and action by another cause which is also finite and has a determinate existence; and again this cause cannot exist nor be determined to action unless by another cause which is also finite and determined to existence and action, and so on, ad infinitum. (shrink)

We contend that it is possible to argue reasonably for and against arguments from classifications and definitions, provided they are seen as defeasible (subject to exceptions and critical questioning). Arguments from classification of the most common sorts are shown to be based on defeasible reasoning of various kinds represented by patterns of logical reasoning called defeasible argumentation schemes. We show how such schemes can be identified with heuristics, or short-cut solutions to a problem. We examine a variety of arguments of (...) this sort, including argument from abductive classification, argument from causal classification, argument from analogy-based classification and arguments from classification based on generalizations. (shrink)

The design, maintenance and use of all measuring instruments involve indicators of the thing, property, or event they are expected to detect or measure. And every quantitative indicator is a functional relation between imperceptible and perceptible facts—for example, the “flow” of time and the rotation of a watch’s hands. The empirical test of any quantitative hypothesis involves the translation of the unobservable variables occurring in it into the observable variable(s) in the indicator hypothesis. Yet, indicators have escaped the notice of (...) nearly all philosophers of science—a fact that may indicate unfamiliarity with laboratory work. (shrink)

The paper reviews criteria which have been used to distinguish science from nonscience and from pseudo–science, and it examines the extent to which they can usefully be applied to “creation science.” These criteria do not force a clear decision, especially as creation science resembles important eighteenth–century forms of orthodox science. Nevertheless, the proponents of creation science may be accused of pious fraud in failing to concede in their political battles that their “science” is tentative and tendentious and will continue to (...) be so while it remains archaic and poorly integrated into the rest of science. (shrink)

Eliminative functionalism is the view that mental attributes, of humans and other machines, consist ultimately in behavioural abilities or dispositions. Hence, ‘Strong AI’: if a machine consistently acts as if it were fully conscious, then conscious it is. From these assumptions, optimistic futurists have derived a variety of remarkable visions of our ‘post-human’ future; from widely-recognised ‘robot rights’ to ‘mind uploading’, immortality, ‘apotheosis’ and beyond. It is argued here, however, that eliminative functionalism is false; for at least on our present (...) knowledge, the subjectively qualitative characteristics of conscious experience are neither deducible from, nor logically required to generate, the performance of any sort of overtly ‘intelligent’, or indeed, characteristically human behaviour. Thus, a machine could easily be designed to report awareness of phenomenal qualities, without necessarily possessing them; and Alan Turing’s ‘Imitation Game’ test for artificial thinking is unable to determine whether or not a machine is sentient. An alternative test is proposed, in which the machine is asked phenomenological questions under conditions designed to detect any form of cheating—whilst also, potentially revealing evidence for the occurrence of genuine qualitative experience. (shrink)

Recent debates on the nature of preferences in economics have typically assumed that they are to be interpreted either as behavioural regularities or as mental states. In this paper I challenge this dichotomy and argue that neither interpretation is consistent with scientific practice in choice theory and behavioural economics. Preferences are belief-dependent dispositions with a multiply realizable causal basis, which explains why economists are reluctant to make a commitment about their interpretation.

What powered Einstein’s discoveries? Was it asking naïve questions, stubbornly? Was it a mischievous urge to break rules? Was it the destructive power of operational thinking? It was none of these. Rather, Einstein made his discoveries through lengthy, mundane investigations, pursued with tenacity and discipline. We have been led to think otherwise in part through Einstein’s brilliance at recounting in beguilingly simple terms a few brief moments of transcendent insight; and in part through our need to find a simple trick (...) underlying his achievements. These ideas are illustrated with the examples of Einstein’s 1905 discoveries of special relativity and the light quantum. (shrink)

This paper asks (a) how new scientific objects of research are onceptualized at a point in time when little is known about them, and (b) how those conceptualizations, in turn, figure in the process of investigating the phenomena in question. Contrasting my approach with existing notions of concepts and situating it in relation to existing discussions about the epistemology of experimentation, I propose to think of concepts as research tools. I elaborate on the conception of a tool that informs my (...) account. Narrowing my focus to phenomena in cognitive neuropsychology, I then illustrate my thesis with the example of the concept of implicit memory. This account is based on an original reconstruction of the nature and function of operationism in psychology. (shrink)

The present note is intended to draw the reader's attention to the analysis of the relation between Newtonian Mechanics and Special Relativity Mechanics (henceforth to be referred to as NM and SRM), given by Philipp Frank, one of the classics of Logical Empiricism (in Frank [1938]). Frank's analysis of the relation between NM and SRM is interesting in many ways. Firstly, it shows clearly that problems of disruptive changes and of conceptual disparity were known to and discussed by Logical Empiricists (...) and that, therefore, some of them at least were not at all blinded to 'dynamic' problems of changes in actual science by their view of physical theories as interpreted axiomatic systems and did not deal with those theories as 'static, frozen in logical mold'. Secondly, it reveals some of the reasons for the Logical Empiricist rejection of what came to be known later as the incommensurability claim. (shrink)

I review the philosophical literature on the question of when two physical theories are equivalent. This includes a discussion of empirical equivalence, which is often taken to be necessary, and sometimes taken to be sufficient, for theoretical equivalence; and "interpretational" equivalence, which is the idea that two theories are equivalent just in case they have the same interpretation. It also includes a discussion of several formal notions of equivalence that have been considered in the recent philosophical literature, including definitional equivalence (...) and categorical equivalence. The article concludes with a brief discussion of the relationship between equivalence and duality. (shrink)

This paper was written with two aims in mind. A large part of it is just an exposition of Tarski’s theory of truth. Philosophers do not agree on how Tarski’s theory is related to their investigations. Some of them doubt whether that theory has any relevance to philosophical issues and in particular whether it can be applied in dealing with the problems of philosophy (theory) of science. In this paper I argue that Tarski’s chief concern was the following question. Suppose (...) a language L belongs to the class of languages for which, in full accordance with some formal conditions set in advance, we are able to define the class of all the semantic interpretations the language may acquire. Every interpretation of L can be viewed as a certain structure to which the expressions of the language may refer. Suppose that a specific interpretation of the language L was singled out as the intended one. Suppose, moreover, that the intended interpretation can be characterized in a metalanguage L +. If the above assumptions are satisfied, can the notion of truth for L be defined in the metalanguage L + and, if it can, how can this be done? Many students of Tarski’s conception will find the above exposition inconsistent with their own views on the essence of Tarski’s conception. On the other hand, as it is argued in this paper, the proposed interpretation of Tarski’s ideas allows one to use Tarski’s theory as a fundamental tool for semantic analyses of various theories, factual theories in particular. More specifically, it is argued that Tarski’s theory of truth allows one to clearly oppose a theory meant to be certain deductive system (a set of accepted sentences, say axioms, and a logical machinery for deducing from them new ones) and a theory meant to be a certain semantic system, i.e a set of sentences that serve to communicate some states of affairs and to use that opposition to explicate and occasionally also define the notion of truth. The opposition in question is of the utmost significance for analyzing some developments in both mathematics and factual sciences. The approach which is concerned with the logical relations between the elements of science such an approach is throughout this paper called analytical is put into question. The growth of science is determined by how well scientific theories are able to account for factual states of affairs. The intuitive notion of truth applied by the scientists does not necessarily correspond in a straightforward way to its Tarskian counterpart. On the other hand, as is claimed in this paper, the Tarskian notion of truth offers as adequate explication of intuitive notion of truth as possible. (shrink)

In this paper we attempt to understand the intellectual origins of Albert Ellis' Rational Psychotherapy (now known as Rational Emotive Behavior Therapy). In his therapeutic practice Ellis used a 'lumper' argument to replace the focus of change in psychoanalysis: not the lengthy uncovering and reworking of the individual's personal history, but the demands in self-talk through which the client is currently dis turbed. In constructing around this the persuasive (rhetorical) package that became his therapy, Ellis drew on a number of (...) popular intellectual movements, operationalism, General Semantics, the holistic theory of emotion, cognitive psychology, and psychoanalysis itself. (shrink)

In their rich and intricate paper ‘Independence, Invariance, and the Causal Markov Condition’, Daniel Hausman and James Woodward ([1999]) put forward two independent theses, which they label ‘level invariance’ and ‘manipulability’, and they claim that, given a specific set of assumptions, manipulability implies the causal Markov condition. These claims are interesting and important, and this paper is devoted to commenting on them. With respect to level invariance, I argue that Hausman and Woodward's discussion is confusing because, as I point out, (...) they use different senses of ‘intervention’ and ‘invariance’ without saying so. I shall remark on these various uses and point out that the thesis is true in at least two versions. The second thesis, however, is not true. I argue that in their formulation, the manipulability thesis is patently false and that a modified version does not fare better. Furthermore, I think their proof that manipulability implies the causal Markov condition is not conclusive. In the deterministic case it is valid but vacuous, whereas it is invalid in the probabilistic case. 1 Introduction 2 Intervention, invariance and modularity 3 The causal Markov condition: CM1 and CM2 4 From MOD to the causal Markov condition and back 5 A second argument for CM2 6 The proof of the causal Markov condition for probabilistic causes 7 ‘Cartwright's objection’ defended 8 Metaphysical defenses of the causal Markov condition 9 Conclusion. (shrink)

In Fechner's psychophysics, the 'mental' and the 'physical' were conceived as two phenomenal domains, connected by functional relations, not as two ontologically different realms. We follow the path from Fechner's foundational ideas and Mach's radical programme of a unitary science to later approaches to primary, psychophysically neutral experience (phenomenology, protophysics). We propose an 'integral psychophysics' as a mathematical study of law-like, invariant structures of primary experience. This approach is illustrated by a reinterpretation of psychophysical experiments in terms of perceptual situations (...) involving a constructed apparatus and an instructed subject. The problematic notion of 'measurement of sensation' is thus eliminated: 'sensations' are merely indices for classes of perceptually equivalent configurations (states of the apparatus) specified by the instruction. The locus of the measured is in the inter-subjectively shared, communicable world—not inside the subject's mind. Finally we discuss the role of integral psychophysics as a scientia prima , logically and methodically preceding physics and psychology. (shrink)

Ciertas interpretaciones de la obra de Kuhn subrayan su contribución inconsciente al positivismo lógico, lo que es consecuencia de un conocimiento y una crítica superficiales de dicha corriente por su parte. En este artículo critico dicha tesis a partir de un texto inédito de Kuhn: The Quest for Physical Theory (1951), sus conferencias en el Instituto Lowell de Boston y una primera presentación del punto de vista de The Structure of Scientific Revolutions.