model-checker 0.3.24

A hyperintensional theorem prover for modal, counterfactual conditionals, constitutive explanatory, and extensional operators.

Model Checker

This project draws on the Z3 theorem prover to provide tooling for finding countermodels for claims which include modal, counterfactual conditional, constitutive explanatory, and extensional operators. The language currently includes the following operators:

• neg for negation
• not for exclusion
• wedge for conjunction
• vee for disjunction
• rightarrow for material conditional
• leftrightarrow for material biconditional
• Box for necessity
• Diamond for possibility
• boxright for must counterfactual conditional
• circleright for might counterfactual conditional
• leq for ground
• sqsubseteq for essence
• equiv for propositional identity

Accessible installation instructions are provided in the GitHub repository.

Instructions

To generate a test file run model-checker in the terminal without arguments. Alternatively, run model-checker path/to/test_file.py if the test_file.py already exists. A number of examples are provided in the GitHub repository.

Each file must specify a set of premises which are treated conjunctively, conclusions which are treated disjunctively, and the number N of atomic states to include in each model. If unspecified, premises = [], conclusions = [], and N = 3 will be set by default. Optionally, the user can specify whether to print the Z3 constraints when a model is found, or the unsatisfiable core when no model exists, as well as an option to save or append the output. These settings are specified with the Boolean values True and False:

• Print all Z3 constraints if a model is found: print_cons_bool
• Print the Z3 unsatisfiable core constraints if no model exists: print_unsat_core_bool
• Print all states including impossible states: print_impossibe_states_bool
• Prompt the user to append the output to the current file in a new file: save_bool

Users can override these settings by including the following flags:

• Include -c to include Z3 constraints.
• Include -i to print impossible states.
• Include -s to prompt the user to save the output in a new file.

Users can print help information, the current version, and upgrade to the latest version with the following flags:

• Include -h to print help information about the programs usage.
• Include -v to print the installed version number.
• Include -u to upgrade to the latest version.

Hyperintensional Semantics

The semantics included is hyperintensional insofar as sentences are evaluated at states which may be partial rather than total as in intensional semantic theories. States are modeled by bitvectors of a specified length (e.g., #b00101 has length 5), where state fusion is modeled by the bitwise OR operator |. For instance, #b00101 | #b11001 = #b11101. The atomic states have exactly one occurrence of 1 and the null state has no occurrences of 1. The space of states is finite and closed under fusion.

States are named by lowercase letters for the sake of printing readable countermodels. Fusions are printed using . so that a.b is the fusion of the states a and b. A state a is part of a state b just in case a.b = b. States may be either possible or impossible where the null state is required to be possible and every part of a possible state is possible. The states a and b are compatible just in case a.b is possible. A world state is any state that is both possible and includes every compatible state as a part.

Sentences are assigned verifier states and falsifier states where both the verifiers and falsifiers are required to be closed under fusion. A sentence is true at a world state w just in case w includes a verifier for that sentence as a part and false at w just in case w includes a falsifier for that sentence as a part. In order to ensure that sentence letters have at most one truth-value at each world state, a fusion a.b is required to be impossible whenever a is verifier for a sentence letter A and b is a falsifier for A. Additionally, sentence letters have at least one truth-value at each world state by requiring every possible state to be compatible with either a verifier or falsifier for any sentence letter.

A negation sentence is verified by the falsifiers for the sentence negated and falsified by the verifiers for the sentence negated. A conjunctive sentence is verified by the pairwise fusions of verifiers for the conjuncts and falsified by falsifiers for either of the conjuncts or fusions thereof. A disjunctive sentence is verified by the verifiers for either disjunct or fusions thereof. Conjunction and disjunction are dual operators obeying the standard idempotent and De Morgan laws. The absorption laws do not hold, nor does conjunction distribute over disjunction, nor vice versa. For a defense of the background theory of hyperintensional propositions, see this paper.

A necessity sentence Box A is true at a world just in case every world state includes a part that verifies A, where a possibility sentence Diamond A is true at a world just in case some world state includes a part that verifies A. Given a world state w and state s, an s-alternative to w is any world state to include as parts both s and a maximal part of w that is compatible with s. A must counterfactual conditional sentences A boxright B is true at a world state w just in case its consequent is true at any s-alternative to w for any verifier s for the antecedent of the counterfactual. A might counterfactual conditional sentences A boxright B is true at a world state w just in case its consequent is true at any s-alternative to w for any verifier s for the antecedent of the counterfactual. The semantic theory for counterfactual conditionals is motivated and further elaborated in this draft. This account builds on Fine 2012.

A grounding sentence A leq B may be read 'A is sufficient for B' and essence sentence A sqsubseteq B may be read 'A is necessary for B'. An propositional identity sentence A equiv B may be read 'A just is for B'. The semantics for ground requires every verifier for the antecedent to be a verifier for the consequent, any fusion of a falsifier for the antecedent and consequent to be a falsifier for the consequent, and any falsifier for the consequent to have a part that falsifies the antecedent. The semantics for essence requires every fusion of a verifier for the antecedent and consequent to be a verifier for the consequent, any verifier for the consequent must have a part that verifies the antecedent, and every falsifier for the antecedent to be a falsifier for the consequent. The semantics for propositional identity requires the two arguments to have the same verifiers and falsifiers. All three constitutive operators are interdefinable where A leq B := neg A sqsubseteq neg B := (A vee B) equiv B, A sqsubseteq B := neg A leq neg B := (A wedge B) equiv B, and A equiv B := (A leq B) wedge (B leq A) := (A sqsubseteq B) wedge (B sqsubseteq A). Instead of a Boolean lattice as in intensional semantics theories, the space of hyperintensional propositions forms a non-interlaced bilattice as described in this paper, building on Fine 2017.

More information can be found in the GitHub repository.