Full Idea
The Deduction Theorem is what licenses a system of 'natural deduction' in the first place.
Gist of Idea
The Deduction Theorem is what licenses a system of natural deduction
Source
David Bostock (Philosophy of Mathematics [2009], 7.2)
Book Reference
Bostock,David: 'Philosophy of Mathematics: An Introduction' [Wiley-Blackwell 2009], p.202
Related Ideas
Idea 15341 Deduction Theorem: ψ only derivable from φ iff φ→ψ are axioms [Horsten]
Idea 13524 Deduction Theorem: T∪{P}|-Q, then T|-(P→Q), which justifies Conditional Proof [Wolf,RS]
Idea 13615 'Conditonalised' inferences point to the Deduction Theorem: If Γ,φ|-ψ then Γ|-φ→ψ [Bostock]