logical.day

Where thought finds its architecture

Premises

Before structure, there is only the raw material of thought — scattered, unexamined, waiting.

P Q ¬

Formal Structure

Ideas find their place — stacked, interlocking, each supporting the next like basalt columns.

Axiom
P → P

The law of identity: a proposition implies itself. The simplest truth, the foundation upon which all reasoning rests.

Theorem
¬(P ∧ ¬P)

Non-contradiction — no statement can be simultaneously true and false. The bedrock principle that makes discourse possible.

Axiom
P ∨ ¬P

Excluded middle. Every proposition is either true or its negation is true. There is no third possibility in classical logic.

Lemma
(P → Q) → (¬Q → ¬P)

Contraposition. If the consequent falls, so falls the antecedent. Every implication carries its shadow.

Definition
∀x(Fx → Gx)

Universal generalization — what holds for all, holds for each. The bridge from the specific to the general.

Theorem
∃x(Fx) ↔ ¬∀x(¬Fx)

Existential equivalence. To say something exists is to deny universal absence.

Corollary
((P → Q) ∧ P) → Q

Modus ponens — the engine of deduction. Given an implication and its premise, the conclusion follows inexorably.

Axiom
P → (Q → P)

The principle of simplification. A true statement remains true regardless of what precedes it in implication.

Lemma
(P → (Q → R)) → ((P → Q) → (P → R))

Distribution of implication. The chain of reasoning can be decomposed and recomposed without loss of truth.

Definition
P ↔ Q ≡ (P → Q) ∧ (Q → P)

Biconditional — the symmetry of equivalence. Two truths that entail each other become indistinguishable in logical space.

Theorem
¬(∀x Fx) → ∃x(¬Fx)

If not everything satisfies a predicate, then there exists a counterexample. The power of negating universals.

Corollary
((P → Q) ∧ (Q → R)) → (P → R)

Hypothetical syllogism — the transitivity of implication. Chains of reasoning link into unbroken sequences of truth.

Derivation

From axioms to theorems, thought flows like water — each step following from the last with the certainty of gravity.

¬ ¬
1. P → Q (Premise)
2. Q → R (Premise)
3. P (Assumption)
4. Q (Modus Ponens, 1, 3)
5. R (Modus Ponens, 2, 4)
6. P → R (Conditional Proof, 3–5)
Quod Erat Demonstrandum

Clarity

The logical day begins not with sunrise, but with the moment a mind recognizes its own capacity for structured thought. Every proposition examined, every inference validated, every contradiction resolved — these are the hours of a logical day.

Therefore, we reason.