PSC Discussion Papers Series Volume 14 | Issue 3 Article 1 5-2000 Explaining Human Fertility: One Theory or Many Theories? Thomas K. Burch University of Western Ontario, [email protected] Follow this and additional works at: https://ir.lib.uwo.ca/pscpapers Recommended Citation Burch, Thomas K. (2000) "Explaining Human Fertility: One Theory or Many Theories?," PSC Discussion Papers Series: Vol. 14 : Iss. 3 , Article 1. Available at: https://ir.lib.uwo.ca/pscpapers/vol14/iss3/1 ISSN 1183-7284 Explaining Human Fertility: One Theory or Many Theories? by Thomas K. Burch Discussion Paper no. 00-3 May 2000 On the web in PDF format: http://www.sscl.uwo.ca/sociology/popstudies/dp/dp00-3.pdf Population Studies Centre University of Western Ontario London CANADA N6A 5C2 Explaining Human Fertility: One Theory or Many Theories?1 Thomas K. Burch Population Studies Centre University of Western Ontario London, Ontario, Canada N6A 5C2 [First draft, 21 March 2000; minor revisions 3 May 2000]] ‘The problem is not with current scientific theories of the world, but with current theories…of what it is to acquire good scientific theories of the world. As is typically the case for individuals, our collective self-knowledge lags behind our collective knowledge of the world.’ Ronald N. Giere, Science Without Laws. ‘Models are to be used, but not to be believed.’ Henri Theil, quoted in Thomas H. Wonnacott and Ronald C. Wonnacott, Introductory Statistics for Business and Economics [3rd ed.]. Introduction This paper is as much about the form of fertility theory as its substance. The central argument is that over the last decades, demography’s quest for better fertility theories has been hampered by a narrow and constricting view of what theory is, how it is constructed, how it is to be judged, and how it is used. Without detailed evidence -- to the best of my knowledge, the research that would yield such evidence has not been done -- I observe that the discipline has been dominated by the methodological thinking of logical positivism, with intellectual roots tracing back to figures such as Karl Pearson, but most directly influential in the mid-century codifications of Ernest Nagel and Carl Hempel. Demographic thinking on theory has also contained large doses of Karl Popper’s doctrine of ‘falsificationism,’ reinforced by a habitual use of statistical tests to ‘accept’ or ‘reject’ hypotheses. According to this methodological approach, theory is built on valid empirical generalisations. And an otherwise appealing theory can be called into question, or even rejected, in the face of empirical exceptions or counter-examples. Demography’s adherence to these philosophical 1. This is a slightly revised version of a paper presented in Session #77, The Status of Fertility Theories, Chair, Geoffrey McNicoll, Population Association of America Annual Meetings, Los Angeles, California, 23-25 March 2000. Research underlying this paper has been supported by a grant from the Social Sciences and Humanities Research Council [Ottawa]. 1 doctrines has discouraged the construction and development of new theoretical models, and led to an under-valuation of a large fortune of theoretical capital in the discipline. A central feature of this under-valuation has been the relegation of large parts of formal demography, those dealing with substantive models of population dynamics, to the status of ‘techniques’ or ‘demographic accounting.’ Demography could benefit from a re-orientation of its thinking about theory. A fruitful alternative approach is to be found in what is known as the ‘semantic’ school of philosophy of science. This view emphasises that all theories are abstract -- and therefore simplified -- representations of some part of the real world. Theories are constructed by the human mind; they do not represent the discovery of natural laws of reality, put there by Nature or by some divine lawgiver. They are not absolute truth. By the same token, they are not false just because they do not accord with certain empirical facts. Since theories are formal systems [whether in words and logic or in mathematics], they are false only if they are logically false. Their empirical ‘validity’ is a matter of context and purpose. A theory is a good theory if it fits reality a] closely enough b] in certain respects c] for the purpose at hand. In the sections to follow, I summarise this alternative view of methodology and theory, and discuss its implications for our understanding of demographic theory in general and fertility theory in particular. I shall briefly discuss the relationship of these ideas to Wilson’s recent expressions of concern over ‘reification’ in demography, and to Lesthaeghe’s discussion of the ideas of Lakatos and Cohen in relation to demographic theory. In closing, I offer a sketch of fertility theories for the 21st century, with an emphasis on the plural. We may or may not develop a ‘unified’ or ‘unitary’ of fertility. But we had better keep our existing theoretical toolkit close at hand, with all our tools sharply honed and well-oiled. 1. Competing Methodological Views of Theory 1.1 Logical Positivism and Falsificationism in Demography My claim that demographers by and large have been logical positivists in their approach to theory is not easy to document. We tend not to be self-conscious and explicit about scientific methodology [philosophy of science] as opposed to method in the narrower sense of technique. And I know of no systematic work examining the implicit methodology used in demographic research in the last half-century. By necessity today I shall argue by means of illustration and anecdote. Before that, two qualifications are in order. The first is that my remarks do not apply so much to economic demography, since economists have a view of theory somewhat different from that of the other social and behavioural sciences, although certainly affected by logical positivism and the ideas of Potter. But the treatment of economics requires another paper. Second, it may be that many of my younger colleagues in demography have already been liberated from logical positivism. To the extent that is so, the problem may be solving itself through cohort succession. Demography’s preoccupation with empirical generalisations as the foundation of theory is nowhere more evident than in our treatment of classic transition theory. As more and more cases of transition have been documented in more and more detail, there has been a tendency to question its 2 status as theory, or even as a rough empirical generalisation. The European Historical Fertility Study out of Princeton was a landmark in this respect. Discovery of cases in which fertility declined at the same time as [or in a few cases even earlier] than mortality, or the absence of strong correlations between fertility decline and standard development variables in others, often were taken as grounds for the dismissal of transition theory as theory. The fact that the older theory could not predict timing or pace of fertility decline was taken to mean it needed to be replaced by a new theory. In his ‘reconsideration’ of the demographic transition, Coale [1973] reviews the evidence and then turns to ‘the generalization that remains.’ His new formulation gives the well-known three preconditions for marital fertility decline, while asserting that one or more of them may occur in the absence of modernisation -- ‘in premodern societies.’ This would seem to be at odds with classic transition theory, which emphasised socio-economic development and modernisation as the driving forces behind fertility decline. But it is difficult to know just what theoretical implications Coale intended, partly because nowhere in the article [whether in reference to Notestein’s earlier work or his own] does call use the word theory. He speaks of the ‘idea of the demographic transition’ or the ‘basic ideas of the transition’ [p.53] but not ‘theory.’ At one point he asks whether the basic ideas ‘are as valid and germane in the contemporary world as they seemed to be when they first became popular’ [p.53]. This apparent throwaway line points to a fundamental distinction on which this paper turns: the distinction between validity and applicability of a theory. I return to this point later. Another example is from the classic paper by Cleland and Wilson [1987]. In their broadside against economic theories of fertility decline, they offer ‘counter-examples of moderate mortality but little or no fertility decline [p.18]. And they conclude ‘the evidence for England contradicts most major theories of transition’ [p.15]. Since a counter-example can only falsify a truly universal statement, it must be that they are thinking of theory based on universal empirical generalisations. And clearly they are following a Popperian approach to theory testing: in this case, they reject economic theories as invalid, contradicted by the evidence. If I seem critical on this point, I am critical also of myself, since as late as my 1996 paper in The Sociological Quartlerly, I argued for formalisation of theory in order to make it falsifiable. Even in cases where a more eclectic, pluralist view of theory is expressed, the notion of eventual falsification of rival theories lingers. Summarising a review article by Massey et al. [1994] on migration theory Weeks comments: ‘Their conclusion was that each of the theories is supported in some way or another by the available evidence and, in particular, none of the theories is specifically refuted. This serves only to underscore the point…that migration is a very complex process. No single theory seems able to capture all of its nuances’ [1999, p.248]. Massey et al. comment that ‘each theory captures an element of truth,’ but they associate this with a ‘characteristic defect in research….an absence of evidence, not the presence of contrary evidence’ [1994, p.739].