Suppose that a sign at the entrance of a hotel reads: “Don’t enter these premises unless you are accompanied by a registered guest”. You see someone who is about to enter, and you tell her: “Don’t enter these premises if you are an unaccompanied registered guest”. She asks why, and you reply: “It follows from what the sign says”. It seems that you made a valid inference from an imperative premise to an imperative conclusion. But it also seems that imperatives (...) cannot be true or false, so what does it mean to say that your inference is valid? It cannot mean that the truth of its premise guarantees the truth of its conclusion. One is thus faced with what is known as “Jørgensen’s dilemma” (Ross 1941: 55-6): it seems that imperative logic cannot exist because logic deals only with entities that, unlike imperatives, can be true or false, but it also seems that imperative logic must exist. It must exist not only because inferences with imperatives can be valid, but also because imperatives (like “Enter” and “Don’t enter”) can be inconsistent with each other, and also because one can apply logical operations to imperatives: “Don’t enter” is the negation of “Enter”, and “Sing or dance” is the disjunction of “Sing” and “Dance”. A standard reaction to this dilemma consists in basing imperative logic on analogues of truth and falsity. For example, the imperative “Don’t enter” is satisfied if you don’t enter and is violated if you enter, and one might say that an inference from an imperative premise to an imperative conclusion is valid exactly if the satisfaction (rather than the truth) of the premise guarantees the satisfaction of the conclusion. But before getting into the details, more needs to be said on what exactly imperatives are. (shrink)

I argue that imperatives express contents that are both cognitively and semantically related to, but nevertheless distinct from, modal propositions. Imperatives, on this analysis, semantically encode features of planning that are modally specified. Uttering an imperative amounts to tokening this feature in discourse, and thereby proffering it for adoption by the audience. This analysis deals smoothly with the problems afflicting Portner's Dynamic Pragmatic account and Kaufmann's Modal account. It also suggests an appealing reorientation of clause-type theorizing, in which the cognitive (...) act of updating on a typed sentence plays a central role in theorizing about both its semantics and role in discourse. (shrink)

Shared agency is a distinctive kind of sociality that involves interdependent planning, practical reasoning, and action between participants. Philosophical reflection suggests that agents engage in this form of sociality when a special structure of interrelated psychological attitudes exists between them, a set of attitudes that constitutes a collective intention. I defend a new way to understand collective intention as a combination of individual conditional intentions. Revising an initial statement of the conditional intention account in response to several challenges leads to (...) a specification of the properties these intentions need to have in order to be genuine commitments. I then show how a structure of conditional intentions with these properties settles a collection of agents on engaging in social interactions that display all the features typically associated with shared agency. (shrink)

Besides pure declarative arguments, whose premises and conclusions are declaratives (“you sinned shamelessly; so you sinned”), and pure imperative arguments, whose premises and conclusions are imperatives (“repent quickly; so repent”), there are mixed-premise arguments, whose premises include both imperatives and declaratives (“if you sinned, repent; you sinned; so repent”), and cross-species arguments, whose premises are declaratives and whose conclusions are imperatives (“you must repent; so repent”) or vice versa (“repent; so you can repent”). I propose a general definition of argument (...) validity: an argument is valid exactly if, necessarily, every fact that sustains its premises also sustains its conclusion, where a fact sustains an imperative exactly if it favors the satisfaction over the violation of the imperative, and a fact sustains a declarative exactly if, necessarily, the declarative is true if the fact exists. I argue that this definition yields as special cases the standard definition of validity for pure declarative arguments and my previously defended definition of validity for pure imperative arguments, and that it yields intuitively acceptable results for mixed-premise and cross-species arguments. (shrink)

Besides pure declarative arguments, whose premises and conclusions are declaratives, and pure imperative arguments, whose premises and conclusions are imperatives, there are mixed-premise arguments, whose premises include both imperatives and declaratives, and cross-species arguments, whose premises are declaratives and whose conclusions are imperatives or vice versa. I propose a general definition of argument validity: an argument is valid exactly if, necessarily, every fact that sustains its premises also sustains its conclusion, where a fact sustains an imperative exactly if it favors (...) the satisfaction over the violation proposition of the imperative, and a fact sustains a declarative exactly if, necessarily, the declarative is true if the fact exists. I argue that this definition yields as special cases the standard definition of validity for pure declarative arguments and my previously defended definition of validity for pure imperative arguments, and that it yields intuitively acceptable results for mixed-premise and cross-species arguments. (shrink)

"Surrender; therefore, surrender or fight" is apparently an argument corresponding to an inference from an imperative to an imperative. Several philosophers, however (Williams 1963; Wedeking 1970; Harrison 1991; Hansen 2008), have denied that imperative inferences exist, arguing that (1) no such inferences occur in everyday life, (2) imperatives cannot be premises or conclusions of inferences because it makes no sense to say, for example, "since surrender" or "it follows that surrender or fight", and (3) distinct imperatives have conflicting permissive presuppositions (...) ("surrender or fight" permits you to fight without surrendering, but "surrender" does not), so issuing distinct imperatives amounts to changing one's mind and thus cannot be construed as making an inference. In response I argue inter alia that, on a reasonable understanding of 'inference', some everyday-life inferences do have imperatives as premises and conclusions, and that issuing imperatives with conflicting permissive presuppositions does not amount to changing one's mind. (shrink)

This paper generalises classical revision theory of the AGM brand to sets of norms. This is achieved substituting input/output logic for classical logic and tracking the changes. Operations of derogation and amendment—analogues of contraction and revision—are defined and characterised, and the precise relationship between contraction and derogation, on the one hand, and derogation and amendment on the other, is established. It is argued that the notion of derogation, in particular, is a very important analytical tool, and that even core deontic (...) concepts such as that of permission resists a satisfactory analysis without it. By way of illustration the last section of the paper analyses the much debated concept of positive permission, of which there turns out to be more than one kind. (shrink)

Mīmāṁsā, an Indian hermeneutics provides an exhaustive methodology to interpret Vedic statements. A formalism namely, Mīmāṁsā Inspired Representation of Actions has already been proposed in a preliminary manner. This paper expands the formalism logically and includes Syntax and Semantics covering Soundness and Completeness. Here, several interpretation techniques from Mīmāṁsā have been considered for formalising the statements. Based on these, instructions that denote actions are categorized into positive and prohibitive unconditional imperatives and conditional imperatives that enjoin reason, temporal action and goal. (...) These instructions are evaluated to three values S, V and N. If the instruction is executed with the intention of goal, then it acquires the value of S; if the intention of goal is present and the instruction is not executed, then it assumes the value of V; and if there is no intention of goal, then the instruction is evaluated to N. This formalism has also been applied in different computational settings such as AI planning, Robotics, task analysis and classification of natural language instructions. An outline of these applications and the comparison of this formalism with other relevant theories are also presented in this paper. (shrink)

The status of constructivism as a metaethical or metanormative theory is unclear partly due to the lack of a clear semantics for central normative terms such as ‘reason’ and ‘ought’. In a series of recent papers, Sharon Street has attempted to clarify the central commitments of constructivism by focusing on the idea of a practical point of view and what follows from it. We improve upon the informal understanding provided by Street and attempt to provide a semantics for ‘ought’. Our (...) semantics respects the core intuition of the constructivist that normative claims are made true because of our practical commitments as agents and also reflects the constructivist’s commitment to the centrality of practical deliberation to normative truth. On our view, a normative claim of the form ⌜S ought to ϕ⌝ is true if ϕ is entailed from S’s set of evaluative attitudes. We argue that a virtue of our definition is that it allows us to see precisely what is distinctive about constructivism as opposed to realism and expressivism. (shrink)

An argument is usually said to be valid iff it is truth-preserving—iff it cannot be that all its premises are true and its conclusion false. But imperatives (it is normally thought) are not truth-apt. They are not in the business of saying how the world is, and therefore cannot either succeed or fail in doing so. To solve this problem, we need to find a new criterion of validity, and I aim to propose such a criterion.

In this paper, we present an informal introduction to Logical English and illustrate its use to standardise the legal wording of the Automatic Early Termination clauses of International Swaps and Derivatives Association Agreements. LE can be viewed both as an alternative to conventional legal English for expressing legal documents, and as an alternative to conventional computer languages for automating legal documents. LE is a controlled natural language, which is designed both to be computer-executable and to be readable by English speakers (...) without special training. The basic form of LE is syntactic sugar for logic programs, in which all sentences have the same standard form, either as rules of the form conclusion if conditions or as unconditional sentences of the form conclusion. However, LE extends normal logic programming by introducing features that are present in other computer languages and other logics. These features include typed variables signalled by common nouns, and existentially quantified variables in the conclusions of sentences signalled by indefinite articles. Although LE translates naturally into a logic programming language such as Prolog or ASP, it can also serve as a neutral standard, which can be compiled into other lower-level computer languages. (shrink)

In a series of articles, P. Vranas recently proposed a new imperative logic. The strong and weak inferences of this logic are motivated by an appeal to a strong and weak ‘support by reasons’ that transfers from the premisses of an argument to its conclusion. They also combine nonmonotonic and monotonic reasoning patterns. I show that for any moral agent, Vranas’s proposal can be simplified enormously.

Can we employ the property of rationality in establishing what rationality requires? According to a central and formal thesis of John Broome’s work on rational requirements, the answer is ‘no’ – at least if we expect a precise answer. In particular, Broome argues that (i) the property of full rationality (i.e. whether or not you are fully rational) is independent of whether we formulate conditional requirements of rationality as having a wide or a narrow logical scope. That is, (ii) by (...) replacing a wide-scope requirement with a corresponding narrow-scope requirement (or vice versa), we do not alter the situations in which a person is fully rational. As a consequence, (iii) the property of full rationality is unable to guide us in determining whether a rational requirement has a wide or a narrow logical scope. We cannot resolve the wide/narrow scope debate by appealing to a theory of fully rational attitudes. This paper argues that (i), (ii) and (iii) are incorrect. Replacing a wide- with a corresponding narrow-scope requirement (or vice versa) can alter the set of circumstances in which a person is fully rational. The property of full rationality is therefore not independent of whether we formulate conditional requirements of rationality as having a wide or a narrow logical scope. As a consequence, the property of full rationality can guide us in determining what rationality requires – even in cases where we expect a precise answer. (shrink)

This paper articulates an account of imperatives that sensibly supports the idea of a logic of imperative inferences. We rebuke common objections to the very possibility of such a logic, from a perspective based on recent linguistic work on the morphosyntax of imperatives. Specifically, we develop the notion that the content of an imperative sentence includes both a force operator alongside an imperational content to which the force applies. We further argue that this account of the content of imperatives constitutes (...) a plausible and flexible framework to develop a logic of imperative by examining a number of reconstructions of this idea using semantical analogs of widespread modal semantics. After studying the performance of those approaches, we conclude that progress in imperative logic has been hindered by the failure to adopt conflict-tolerant and resource-sensitive semantics, but suggest that such considerations can be incorporated in this flexible framework. Finally, we also propose a simple account of the difference between operators applying to the content of imperatives and imperative operators, in a way that sheds light on some of the issues underlying the usual antinomies. (shrink)

In this paper, I will discuss the various ways in which intentions can be said to be conditional, with particular attention to the internal conditions on the intentions’ content. I will first consider what it takes to carry out a conditional intention. I will then discuss how the distinctive norms of intention apply to conditional intentions and whether conditional intentions are a weaker sort of commitments than the unconditional ones. This discussion will lead to the idea of what I call (...) the ‘deep structure’ of intentions. Roughly, this is the idea that the conditional nature of our intentions is only partially made explicit in the expressions we use to communicate our intentions and in the explicit form of our thinking about and reasoning with them. Most conditions that qualify our intentions are part of a deep functional structure that can be evinced by observing the actual psychological functioning of intentions and by considering the rational requirements that they engage. I will argue that the deep structure of intentions is characteristically conditional. Genuinely unconditional intentions are only limiting instances of conditional intentions and their contribution to agency can only be understood in light of this fact. I will conclude by showing that the characteristic conditional structure of intentions is intimately related to distinctive features of human agency, especially to its unity over time. (shrink)

This paper formalizes part of the cognitive architecture that Kant develops in the Critique of Pure Reason. The central Kantian notion that we formalize is the rule. As we interpret Kant, a rule is not a declarative conditional stating what would be true if such and such conditions hold. Rather, a Kantian rule is a general procedure, represented by a conditional imperative or permissive, indicating which acts must or may be performed, given certain acts that are already being performed. These (...) acts are not propositions; they do not have truth-values. Our formalization is related to the input/ output logics, a family of logics designed to capture relations between elements that need not have truth-values. In this paper, we introduce KL3 as a formalization of Kant’s conception of rules as conditional imperatives and permissives. We explain how it differs from standard input/output logics, geometric logic, and first-order logic, as well as how it translates natural language sentences not well captured by first-order logic. Finally, we show how the various distinctions in Kant’s much-maligned Table of Judgements emerge as the most natural way of dividing up the various types and sub-types of rule in KL3. Our analysis sheds new light on the way in which normative notions play a fundamental role in the conception of logic at the heart of Kant’s theoretical philosophy. (shrink)

J.C. Beall and Greg Restall's Generalised Tarski Thesis is a generalisation of the seemingly diverse conceptions of logical consequence. However, even their apparently general account of consequence makes necessary truth-preservation a necessary condition. Sentences in the imperative mood pose a problem for any truth-preservationist account of consequence, because imperatives are not truth-apt but seem to be capable of standing in the relation of logical consequence. In this paper, I show that an imperative logic can be formulated that solves the problem (...) of imperative consequence by leading naturally to a further generalisation of the GTT. (shrink)

Blackburn has outlined a formal account for moral expressivism, and we argued that the moral Frege-Geach problem can be solved formally by appending two rules for the boo-operator which are missing from his account. We then extended Blackburn’s formal account to generate a similar solution to the problem in modal context and showed that the validity of the modal argument can be preserved too in modal expressivism. However, the higher-order element endorsed by Blackburn does not seem necessary for solving the (...) Frege-Geach problem. Nor is his extension from moral expressivism to modal expressivism tenable, since the latter violates its own ontological constraint. A general moral is drawn on the basis on three observations made in evaluating Blackburn’s expressivism. (shrink)

This article surveys a range of current views on the semantics of imperatives, presenting them as more or less conservative with respect to the Truth-Conditional Paradigm in semantics. It describes and critiques views at either extreme of this spectrum: accounts on which the meaning of an imperative is a modal truth-condition, as well as various accounts that attempt to explain imperative meaning without making use of truth-conditions. It briefly describes and encourages further work on a family of views lying somewhere (...) in the middle. On such views, an imperative will semantically determine, without having as its meaning, a modal truth-condition, which figures centrally in accounting for various aspects of its meaning. (shrink)

In this paper I will develop a view about the semantics of imperatives, which I term Modal Noncognitivism, on which imperatives might be said to have truth conditions (dispositionally, anyway), but on which it does not make sense to see them as expressing propositions (hence does not make sense to ascribe to them truth or falsity). This view stands against “Cognitivist” accounts of the semantics of imperatives, on which imperatives are claimed to express propositions, which are then enlisted in explanations (...) of the relevant logico-semantic phenomena. It also stands against the major competitors to Cognitivist accounts—all of which are non-truth-conditional and, as a result, fail to provide satisfying explanations of the fundamental semantic characteristics of imperatives (or so I argue). The view of imperatives I defend here improves on various treatments of imperatives on the market in giving an empirically and theoretically adequate account of their semantics and logic. It yields explanations of a wide range of semantic and logical phenomena about imperatives—explanations that are, I argue, at least as satisfying as the sorts of explanations of semantic and logical phenomena familiar from truth-conditional semantics. But it accomplishes this while defending the notion—which is, I argue, substantially correct—that imperatives could not have propositions, or truth conditions, as their meanings. (shrink)

In this paper, I focus on the fiction of the retroaction of the condition in contracts, a very old tool of law which may be traced back to Roman antiquity. In the first part, I introduce the notion of a contract with a suspensive condition, i.e. a contract whose efficacy is subordinated to a future uncertain event. As will be addressed in the second part, this kind of contracts is often linked to the fiction of the retroaction of the condition (...) (e.g. the French Code Civile 1179 and the Italian Codice Civile 1360): When the condition of the contract is fulfilled we should do as if the condition was fulfilled at the very time of the stipulation of the contract. In the third part, I turn to an attempt by the young Gottfried Wilhelm Leibniz to rationalize this fiction: Although – as every fiction – false, the retroaction of the condition allows us to reach true conclusions with respect to a deterministic metaphysics. Eventually, after having raised some objections to the Leibnizian account, I develop an alternative rationalization of the fiction: The fiction does indeed lead us to true conclusions because the same conclusions may be reached by relying on an equity-principle or, alternatively, on a merely possible yet expedient law. (shrink)

1 Th. 5:17 tells us to pray without ceasing. Many have worried that praying without ceasing seems impossible. Most address the problem by giving an account of the true nature of prayer. Unexplored are strategies for dealing with the problem that are neutral on the nature of prayer, strategies consistent, for example, with the view that only petition is prayer. In this article, after clarifying the nature of the problem for praying without ceasing, I identify and explore the prospects of (...) five different strategies that are neutral in this sense. I also raise problems for each strategy. (shrink)

This paper provides a proof-theoretic account of imperative logical consequence by generalising Greg Restall’s multiple conclusion bilateralism for declarative logic. According to imperative bilateralism, a sequent Γ ⊢ Δ is valid iff jointly commanding all the imperatives Φ ∈ Γ and prohibiting all the imperatives Ψ ∈ Δ clashes. This account has three main virtues: (1) it provides a proof-theoretic account of imperatives; (2) it does not rely on the controversial notion of imperative inference; and (3) it is neutral regarding (...) cognitivism about imperatives. (shrink)

Non-cognitivism is a variety of irrealism about ethics with a number of influential variants. Non-cognitivists agree with error theorists that there are no moral properties or moral facts. But rather than thinking that this makes moral statements false, noncognitivists claim that moral statements are not in the business of predicating properties or making statements which could be true or false in any substantial sense. Roughly put, noncognitivists think that moral statements have no truth conditions. Furthermore, according to non-cognitivists, when people (...) utter moral sentences they are not typically expressing states of mind which are beliefs or which are cognitive in the way that beliefs are. Rather they are expressing non-cognitive attitudes more similar to desires, approval or disapproval. Cognitivism is the denial of non-cognitivism. Thus it holds that moral statements do express beliefs and that they are apt for truth and falsity. But cognitivism need not be a species of realism since a cognitivist can be an error theorist and think all moral statements false. Still, moral realists are cognitivists insofar as they think moral statements are apt for truth and falsity and that many of them are in fact true. (shrink)

This dissertation examines some of ways of evaluating beliefs, relevant to epistemology and to metaphysics. Some problems in normative epistemology are solved by properly relating justified belief, rational belief, and knowledge. Chapter 1 uses this strategy to defend externalism about justified belief. Chapters 3 and 4 defend the view that knowledge is the epistemic standard we aim for our beliefs to meet. Chapter 2 investigates which beliefs are improper because formed in an objectionably circular way. The findings support the Moorean (...) response to Brain-In-a-Vat skepticism, by rebutting the objection from ‘easy knowledge’. The theory of justified belief developed in chapter 1 underwrites the Moorean reply. Chapters 5 and 6 make a non-epistemic way of evaluating beliefs central to metaphysics. To understand relativity or vagueness in a subject-matter, we must hold that being true or false is not the metaphysically serious evaluation of how a belief answers to reality. Either verdict on a borderline case is ‘acceptable’ in the metaphysically serious sense. For a matter to be relative is for the ‘acceptability’ of affirming the proposition to vary between judges. Chapters 5 and 6 sketch an approach to metaphysics built from the notion of ‘metaphysically acceptable judgment’, with chapter 6 concentrating on vagueness, and chapter 5 focusing on relativism about knowledge. Chapter 5 argues that the lottery and preface puzzles manifest central features of our concept of knowledge. The proposed version of relativism about knowledge is the only theory to respect those features. The view of knowledge presented in chapter 5 is not an isolated metaphysical extravagance, as the same framework is needed for the right metaphysics of everything that’s vague. It is worth noting that my solution to the lottery puzzle is metaphysical relativism about knowledge, but my rebuttal of Brain-In-a-Vat skepticism concerns epistemic circularity and belongs to normative epistemology. Much recent work incorrectly assumes that the two puzzles receive the same treatment. (shrink)

This paper is divided in five sections. Section 11.1 sketches the history of the distinction between speech act with negative content and negated speech act, and gives a general dynamic interpretation for negated speech act. “Downdate semantics” for AGM contraction is introduced in Section 11.2. Relying on semantically interpreted contraction, Section 11.3 develops the dynamic semantics for constative and directive speech acts, and their external negations. The expressive completeness for the formal variants of natural language utterances, none of which is (...) a retraction, has been proved in Section 11.4. The last section gives a laconic answer to the question posed in the title of the paper. (shrink)

Imperative sentences like Dance! do not seem to represent the world. Recent modal analyses challenge this idea, but its intuitive and historical appeal remain strong. This paper presents three new challenges for a non-representational analysis, showing that the obstacles facing it are even steeper than previously appreciated. I will argue that the only way for the non-representationalist to meet these three challenges is to adopt a dynamic semantics. Such a dynamic semantics is proposed here: imperatives introduce preferences between alternatives. This (...) characterization of meaning focuses on what function a sentence serves in discourse, rather than what that sentence refers to (e.g., a state of the world). By representing the meaning of imperatives, connectives and declaratives in a common dynamic format, the challenges posed for non-representationalism are met. (shrink)

This work explores the hypothesis that natural language is a tool for changing a language user's state of mind and, more specifically, the hypothesis that a sentence's meaning is constituted by its characteristic role in fulfilling this purpose. This view contrasts with the dominant approach to semantics due to Frege, Tarski and others' work on artificial languages: language is first and foremost a tool for representing the world. Adapted to natural language by Davidson, Lewis, Montague, et. al. this dominant approach (...) has crystalized as truth-conditional semantics: to know the meaning of a sentence is to know the conditions under which that sentence is true. Chapter 1 details the animating ideas of my alternative approach and shows that the representational function of language can be understood in terms of the more general function of changing representational mental states. Chapters 2-4 argue that the additional resources of this more general conception of meaning allow us to explain certain phenomena involving conditionals and grammatical mood that truth-conditional semantics does not. In the analysis of these specific phenomena and the articulation of the general approach on offer, it emerges that this approach combines insights and benefits from both use-theoretic and truth-theoretic work on meaning. (shrink)

'Post this letter!' does not entail 'Post this letter or drink up my wine!' (the Ross Paradox) because one can be in a state with the content of the former without being in a state with the content of the latter; in turn, because the latter can rationalize drinking up my wine but the former cannot; in turn, because practical rationalization flows toward one's present situation, in contrast with the flow of theoretical rationalization from one's present situation. Formally, this is (...) implemented with a semantics for imperatives involving a partition to set up an issue of significance and a proposition to establish how to settle it. I characterize a series of languages and language-games to implement all this, and appeal to an 'endorsement-theoretic' conception of modals as quantifiers over mental states to explain why 'You must post this letter' does not entail 'You must either post this letter or drink up my wine'. (shrink)

My Ph.D. thesis œImpossibilità nel diritto€ [Impossibility in the Legal Domain] is devoted to the systematic analyses of what are called, at least prima facie, €œlegal impossibilities. My dissertation defines and isolates an area of studies - impossibility in the law - that has never been put organically together. In my work I present some case studies of normative impossibilities and discuss them from a philosophical point of view: impossible laws, impossible norms in a prescriptive theory of norms (ch. 2), (...) conflicting norms and legal gaps (metanormative impossibility - ch. 3), impossible obligations (ch. 4), impossible crimes (ch. 5), impossible legal proofs (ch. 6). I organize my research along the distinction -€“ introduced in ch. 1 -€“ between impossibility of norms (i.e. impossible norms and impossible normative acts) and impossibility from norms (i.e. impossibility due to a norm or a set of norms); the distinction between the impossibility of a norm conceived as a single entity and the impossibility of a norm conceived as part of a legal system; and the distinction of two uses of impossibilities in general, as impossibility can be both the object of a modal qualification and a modality itself. I propose four new contributions to the study of impossibility in the legal domain (ch. 7). Firstly, I reconstruct two different functions of the impossibility in the legal domain (exculpatory and invalidating); secondly, I put forward a triadic model for describing impossibility in the legal domain (in which, roughly, a set of sources of impossibilities is qualified by a function for the assumption of impossibility in the actual and concrete legal system); thirdly, I define and investigate the relationship of creation, assumption and presupposition between impossibility and a legal system; fourthly, I critically list and review all the different kinds of things that are called €˜impossibilities€™ inside a legal system, showing how sometimes the use of the concept of impossibility is not carefully justified. As an appendix (ch. 8), I outline a logic for impossibilities in the legal domain that allows to investigate the phenomena discussed in the work by breaking down the equivalence between being impossible (in the legal domain) and being logically contradictory. (shrink)