Abstract
Most engineering reasoning in practice is about how to achieve some predetermined end. Despite its paramount importance, this form of reasoning has hardly been investigated in the literature.a The aim of this paper is therefore to explore the question to what extent technical norms can be said to have a truth-value, and under what conditions practical inferences are deductively valid. We take technical norms to be sentences of the form ‘If you want A, and you are in a situation B, then you ought to do X’. Von Wright’s standard example of making a hut habitable is our paradigm for practical inferences, where an obligation to act is deduced from an intention to realize an end, and an empirical constraint on how this end can be achieved. Our instrument of analysis is dynamic logic (PDL), since actions are aimed at changing the world. PDL already suffices to provide truth-conditions for technical norms. To accommodate the obligation in practical inferences we draw on John Jules Meyer’s deontic version of PDL. By paraphrasing ‘person P wants’ with ‘person P imposes an obligation on herself,’ we can give a plausible definition of the validity of practical inferences. In the discussion section, we address the issues of the reliability instead of truth-value of technical norms, and of the defeasibility of practical inferences as they occur in engineering practice.
a The work of Yanjing Wang (e.g. 2016) forms the welcome exception to this claim.
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Notes
- 1.
In ‘Practical inference’ Von Wright writes that he deliberately uses the word ‘must’ instead of ‘ought’ because it is “somehow stronger” (1963a, p. 161). His intuitions on this point seem not to have been very clear, however, since elsewhere he downplays this distinction between ‘must’ and ‘ought to’ (e.g. 1963b, p. 101).
- 2.
It could be objected that ‘habitable’ is a concept that involves notions from the intentional domain, but this is not what Von Wright seems to have had in mind, for he writes that the relation between temperature and habitability of a hut “is a causal fact about the living conditions of men” (1963a, p. 160). If we interpret “living conditions” as “physical living conditions”, the second premise articulates a necessity in the physical world. Thus “habitable” should be read here as a physical property rather than a means to get the hut inhabited.
- 3.
Niiniluoto additionally considers other forms of technical norms, which correspond to empirical connections between means and ends that are weaker than necessity, e.g. connections where a means is sufficient but not necessary for an end and connections where a means is only probabilistically sufficient.
- 4.
Von Wright: “A statement to the effect that something is (or is not) a necessary condition of something else I shall call an anankastic statement.” (1963b, p. 10); “Laws of nature and other anankastic propositions are, on the whole, not concerned with action; but these we have decided not to call ‘norms’.” (idem, p. 13).
- 5.
Von Wright characterized his work in the 1960s as “a turn in logic away from a traditional interest in what is, the static, to that which comes to be, the dynamic” (1999, p. 30).
- 6.
cf Meyer et al. (1999).
- 7.
Note that one may also achieve A by satisficing some design criteria. Herbert Simon’s notion does not change our approach fundamentally.
- 8.
Because we look upon actions as a logical category of its own, we do not opt for a STIT logic.
- 9.
In PDL an action α is always successful – it changes a state in a predefined way.
- 10.
A comprehensive discussion of action negation is Broersen (2004).
- 11.
PDL harbors still more operators, but these do not play a role in our analysis.
- 12.
When Meyer, van de Hoek and van Linder apply PDL to formalize the dynamics of beliefs, desires, intentions, commitments, (Meyer et al. 1999) they use a deterministic version of PDL and even in a deterministic context this fine-tuned psychological dynamics turns out to be fairly complicated. To paraphrase engineering knowledge we think as a first approximation we may dispense with these agent specific notions. Engineering means-end knowledge strives to be as least as possible subject-dependent or subjective. We cannot however avoid the nondeterministic version of PDL since engineers often need to choose between different in principle possible actions to achieve their goal.
- 13.
We recognize that in natural language means are often identified with objects or instruments and not actions, but do not think this poses an important objection to our approach. We may always translate the object-as-means language into to the actions the means-object performs. If an ignition coil is the means to cause an ignition in the combustion chamber at exactly the right time, we may rephrase this means as the action of igniting.
- 14.
M α,S denotes the set of states of the world that is the result of performing α in state S.
- 15.
Although this definition seems intuitively plausible, it lacks important relevance conditions. Typically we do not call an action a sufficient means to some end if this end is inevitable anyway, such as, for example, the setting of the sun. According to definition 3.2 all actions which start before sunset and end after sunset are sufficient means for the occurrence of the sunset. There are several attempts to repair this, but for the purposes of the present paper we can ignore this problem (cf. Hughes et al. 2007, p. 215/6).
- 16.
Note that ε need not be atomic but may consist for instance of two subsequent subactions: ε:= ε1; ε2. In such a case O[ε1; ε2] ≡ Oε1 ∧ [ε1]Oε2. (Note that in contrast F[ε1; ε2] ≡ [ε1]Fε2.) This means that V is true in all states along the paths towards the state where the hut is finally heated; only in that final state V is false.
- 17.
- 18.
There are ways for DDeL* to bring out the distinction between voluntary obligations and imposed obligations. Voluntary obligations result from a previous action of the person who has the obligation, namely the action of taking an obligation upon oneself, whereas for imposed obligations the action of imposing the obligation is performed by another person than the person who has the obligation.
- 19.
It is here that the step from the Dynamic-States version to the Action version of PI is actually made.
- 20.
Meyer and others similarly claim that ‘being committed to α’ intuitively corresponds to ‘having promised (to oneself) to perform α next (or at least a.s.a.p.)’ (Meyer et al. 1999, p16). Note, further, that although one may want unattainable things, here we do assume that the things wanted are at least empirically attainable. This is relevant for engineering and will be taken up again in the final Discussion section.
- 21.
See for more technical details Hughes et al. (2007), pp. 225–227.
- 22.
This differs from the claim that for 〈α〉 and [β], α can and β possibly cannot be performed. The reader interested in the logic of effectiveness may consult Harz (2007) (in German).
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Zwart, S., Franssen, M., Kroes, P. (2018). Practical Inference—A Formal Analysis. In: Fritzsche, A., Oks, S. (eds) The Future of Engineering. Philosophy of Engineering and Technology, vol 31. Springer, Cham. https://doi.org/10.1007/978-3-319-91029-1_3
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