Not "That Sounds Right." Proven, or Disproven.
"Plausible" Is Not "Correct"
Language models are pattern matchers. Ask whether a conclusion follows from your premises, or whether a set of rules can all hold at once, and you get a fluent answer that is sometimes wrong in ways that read exactly like being right.
Some questions don't want a probability. They want a proof.
Formal Logic routes those questions to a deterministic solver. Same input, same verdict, every time — with the model or counterexample that justifies it.
How It Actually Works
The upstream LLM translates your question into formal statements, then invokes a solver that returns a definite answer:
tools = [
entails, # Do the conclusions follow from the premises?
is_satisfiable, # Can these constraints all hold at once?
check_consistency, # Does this set of rules contradict itself?
fol_prove, # First-order / propositional proof
ltl_check, # Temporal properties over sequences
]The result is a verdict — entailed / not entailed, satisfiable / unsatisfiable — accompanied by a witness: the assignment that makes it work, or the counterexample that breaks it. No "I think so."
When to Reach for This
- ✓A claim needs to be proven or disproven, not estimated
- ✓You want to check a set of requirements for contradictions
- ✓Correctness matters more than a plausible-sounding answer
- ✓You're verifying that a spec actually entails what you think it does
Use Cases
Requirement Consistency
Prove a set of rules, constraints, or ADRs doesn't contradict itself before you build on top of them.
Policy & Access Logic
Verify that authorization rules entail the access you intend — and provably forbid what they should.
Spec Verification
Confirm a design actually satisfies the properties it claims, with a counterexample when it doesn't.
Other Reasoning Tools
Different failures need different interventions. Pick the right tool for the moment.
Your AI Estimates. This One Proves.
$20/month for entailment, satisfiability, and temporal-logic checks that return a verdict — not a confidence score.