Across space and time, various socioeconomic systems have existed and still exist, each with its own features and characteristics that distinguishes it from other socioeconomic systems. For example, the form of capitalism in the modern Western world is a socioeconomic system distinct from, and presumably much more complex than, the socioeconomic system that shaped tribal life. One could also claim that the socioeconomic system in place in the Scandinavian countries nowadays is a different system than, or at least differs in some significant respects from, the socioeconomic system in current-day United States. Acknowledging this fact raises the following question: is it possible to analyse, explain, and predict phenomena in those different socioeconomic systems by using the same theories and models, or is it necessary to develop different theories and models that each apply to different socioeconomic systems? This is the problem of historical specificity. As Hodgson puts it in How Economics Forgot History (2001), this problem of historical specificity “addresses the limits of explanatory unification in social science: substantially different socioeconomic phenomena may require theories that are in some respects different” (p. 23). Note the ‘in some respects’, for it is likely that different socioeconomic systems still have a number of phenomena in common. Scarcity of resources, to take an example from Hodgson (2001), seems to be a characteristic that many, if not all, socioeconomic systems share.1 The fundamental idea behind historical specificity is that despite those possible commonalities, socioeconomic systems may differ sufficiently to warrant theories and models that are tailored to the socioeconomic system at hand (Hodgson, 2001). Such theories tailored to a specific socioeconomic system or systems are labelled historically sensitive theories; phenomena that are relative to socioeconomic systems are labelled historically sensitive phenomena. This essay intends to contribute to the discussion on whether economic theories and models should be historically sensitive and how such a historically sensitive science of economics may be developed. More precisely, it aims to argue in favour of historically sensitive theories by appealing to the notion of invariance introduced by Woodward (2005). Invariance applies to causal generalizations, and can intuitively be understood as a measure of the extent to which a causal generalization continues to hold under changes in the (putative) cause. For the problem of historical specificity, the most important feature of the notion of invariance is that it is relative to systems. That is, a generalization may be invariant (may hold) in one system, but not in another system. Woodward (2005) argues that theories of causal explanation should require generalizations to be invariant, instead of requiring generalizations to meet the criteria of lawhood. Lawhood refers to the idea that generalizations qualify as law only if they meet certain criteria such as exceptionlessness and universal validity. Based on this, the main claim made in this essay is that adopting the notion of invariance instead of the notion of lawhood provides one with a conceptual-causal framework that naturally incorporates historical specificity, or at least a framework that can deal properly with historical specificity. If Woodward (2005) correctly claims that invariance should replace the notion of lawhood, it follows that historical specificity—or at least relativity to a system or systems—is a natural feature of any causal generalization. In addition to the main claim, this essay shows that even though the problem of historical specificity is nowadays largely forgotten about and even considered obsolete (or so Hodgson (2001) argues), the idea of historically sensitive theories is consistent with some methodological statements of two prominent economists—Milton Friedman and Fritz Machlup. The point of showing this is not to give an additional argument in favour of incorporating historical specificity in economics, but to suggest a strategic way to convince economists of the relevance of this notion. This essay is structured as follows. In section 2, I provide some historical context surrounding the notion of historical specificity. Subsequently, I describe the notion of invariance in section 3. Section 4 studies the relation between historical specificity and invariance and argues that the notion of invariance naturally incorporates the notion of historical specificity. It also shows that the ideas of historical specificity and invariance are reconcilable with the methodological positions (or at least with some methodological statements) of Milton Friedman and Fritz Machlup. The last section concludes.