Chapter 4 further justifies the Universal Partial Defence (UPD) on a paradigmatic plane by exploring the second (political) deficit to which the Real Person Approach (RPA) responds. It deploys the principle of parsimony to explain how the weight afforded to the dominant rational agency account contributes to a form of conceptual punitiveness at culpability evaluation, which is reinforced by a broader culture of responsibilisation. Applying the RPA, the chapter conceptualises punitive excess at culpability evaluation as a form of pathogenic vulnerability, unearthing a discrete version of misrecognition at this site. In response, the recognitive justice feature of the RPA is engaged to consider how we might ameliorate this particular variant of social injustice. Drawing on recent scholarship promoting a more modest approach to criminal responsibility attribution, the principle of parsimony is reauthenticated as a core tenet of the criminal law, supporting the call for a UPD at the doctrinal level.

In this text, Ockham deals with whether memory, intellect, and will are really distinct powers. He answers in the negative. After presenting first Aquinas’, then Henry of Ghent’s, and finally John Duns Scotus’ views in some detail, along with replies, Ockham presents his own uncompromising identity theory of the powers of the soul. Based on the principle of parsimony, he argues that the rational soul is identical to the intellect and the will. By transitivity, this entails that the intellect is identical to the will so that the rational soul is a single power to engage in acts of thinking and and willing. Fleshing out his view, Ockham also gives a sort of rule for knowing when distinct cognitive and appetitive powers must be posited, and when not. According to this rule, if everything outside of a cognizer or desirer remains the same, and the cognizer or desirer is able to have an act of one power, while being unable to have the act of another power, then those powers must be distinct. For example, some people may be unable to see while being able to hear and other people may be unable to hear while being able to see. It follows that sight and hearing must be distinct powers.

The concept of Occam’s Razor, also known as the principle of parsimony, is a motivating force in science. Galileo’s experiment of dropping objects of different weights from atop the Leaning Tower of Pisa to show that they fall at the same rate is an illustration of this principle. But the application of Occam’s Razor to climate modeling is less straightforward. Simple models of the kind used by Manabe provide qualitative insights, but they are not well-suited for quantitative predictions. To understand this, we can make an analogy between the hierarchy of climate models and the hierarchy of biological models, from fruit fly to mouse. Simple models are used to explore “climate tipping points,” where amplifying feedbacks lead to abrupt climate change, but they may not consider all the stabilizing feedbacks. It is therefore important to use a hierarchy of models, with varying degrees of complexity, to study climate phenomena.