Predicate Logic Evaluator
Evaluate quantified predicate logic statements (universal, existential, unique existential) over a finite domain.
About this calculator
This calculator evaluates a quantified statement — universal (for all), existential (there exists), unique existential (exactly one), or negated universal — over a finite domain, working from two counts you supply: how many elements the domain has, and how many of them satisfy the predicate. The Satisfaction Ratio (satisfying elements divided by domain size) appears to respond a bit more to a ten percent nudge on the count of satisfying elements than to the same nudge on domain size — but that ranking is a Math.round() artifact, not a real difference in influence. At the default Elements Satisfying P(x) of 7, a ten percent nudge lands on 7.7 or 6.3, which round to 8 or 6 — an effective swing of a full ±1 out of 7, or about ±14.3%, larger than the ±10% the nudge was supposed to represent. Domain Size (default 10) doesn't get that same inflation: its ten percent nudge lands on 11 or 9, both already whole numbers, so rounding adds nothing extra there.
Strip the rounding out and compare the two inputs on equal footing and Domain Size actually wins narrowly (roughly 0.202 versus 0.200) — the numerator's apparent edge is an artifact of which input's ten-percent nudge happens to round further from its starting value, not a real asymmetry in how the ratio responds to each input. The Quantifier selector itself never touches that ratio at all: Satisfaction Ratio is computed once, before the calculator even looks at which quantifier you picked, so switching between universal and existential changes only the Truth Value output, never the underlying fraction. The Expected Satisfying Pairs figure, used for reasoning about nested quantifiers like "for all x there exists y," is not counted directly — it assumes P(x, y) behaves independently across the domain and estimates the pair count as the domain size squared times the Satisfaction Ratio squared, which can diverge substantially from a real predicate's actual pair count whenever satisfaction is correlated across elements rather than independent.
Inputs
Results
Truth Value (1=True)
0
Satisfaction Ratio
0.7
How to Use This Calculator
- Enter Domain Size and how many Elements Satisfy P(x) — the predicate is represented by these counts, not a typed formula.
- Select the Quantifier: Universal (∀), Existential (∃), Unique Existential (∃!), or Negated Universal (¬∀).
- Review the Truth Value evaluation over the specified domain.
- Review Counterexamples (∀) or Witnesses (∃), and the Expected Satisfying Pairs (∀x∃y) estimate for nested-quantifier reasoning.
- Use the output to verify formal arguments in mathematics or computer science.
What each input means
- Domain Size
- Number of elements in the domain of discourse
- Elements Satisfying P(x)
- How many domain elements make the predicate P true
- Quantifier
- Which quantifier to evaluate over the domain.
How this is calculated
Worked example, using the default values
- Identify Input ParametersDomain Size = 10, Elements Satisfying P(x) = 7, Quantifier = 1 = 3 input(s) provided
- Calculate Truth Value0 = 0
- Calculate Satisfaction RatioSatisfaction Ratio0.7 = 0.7
- Calculate True CountTrue Count = 77 = 7
- Calculate False CountFalse Count3 = 3
Engine last updated . Checked against 4 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does the Quantifier selector not move the Satisfaction Ratio at all?
Satisfaction Ratio is calculated as satisfying elements divided by domain size before the calculator's logic ever branches on which quantifier you chose — it's a plain fraction, not a quantified truth value. The Quantifier only determines the separate Truth Value output, which applies a completely different rule (all, at least one, exactly one, or at least one false) depending on which option is selected.
Why does raising the number of satisfying elements move the ratio more than raising the domain size does?
At the calculator's defaults, it's actually a Math.round() artifact rather than a real difference in pull. A ten percent nudge on Elements Satisfying P(x) (default 7) lands on 7.7 or 6.3, and rounding to the nearest whole element inflates that to a full ±1, or about ±14.3% — bigger than the ten percent the nudge was meant to represent. Domain Size (default 10) doesn't get that same boost, since a ten percent nudge lands on 11 or 9, both already whole numbers with nothing for rounding to distort. Compare the two inputs without that rounding quirk and Domain Size actually edges out Elements Satisfying P(x) narrowly (about 0.202 versus 0.200) — the satisfying-count's apparent lead comes from which input's nudge happens to round further from its starting value, not from any inherent asymmetry between numerator and denominator.
How is Unique Existential different from ordinary Existential?
Existential (there exists) is true as soon as at least one domain element satisfies the predicate, no matter how many others also do. Unique Existential is far stricter — it's only true when the count of satisfying elements equals exactly 1, so a predicate satisfied by two or more elements makes Unique Existential false even though ordinary Existential would still read true.
Can I trust Expected Satisfying Pairs as an exact count for a real predicate?
No — it's a statistical estimate, not a count of anything the calculator has actually verified. It multiplies the domain size squared by the Satisfaction Ratio squared, which assumes satisfaction is independent across every pair of elements; a real predicate where satisfaction clusters together or excludes certain pairs can produce a true pair count well above or below this estimate.
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