Full Idea
If we adopt a justificationist theory of meaning, we must reject the universal law of excluded middle, and with it classical logic (which rests on the two-valued semantics of bivalence). We admit only intuitionist logic, which preserves justifiability.
Clarification
'Justificationist' is Dummett's renaming of the older 'verificationist' theory
Gist of Idea
A justificationist theory of meaning leads to the rejection of classical logic
Source
Michael Dummett (Thought and Reality [1997], 5)
Book Reference
Dummett,Michael: 'Thought and Reality (Gifford Lectures)' [OUP 2006], p.64
A Reaction
This is Dummett's philosophy in a very neat nutshell. He seems to have started by accepting Brouwer's intuitionism, and then working back to language. It all implies anti-realism. I don't buy it.