A context sensitive grammar (CSG) is a grammar where all productions are of the form αAβ → αγβ where γ ≠ ε. During derivation non-terminal A will be changed to γ only when it is present in the context of α  and β.  *Note the constraint that the replacement string γ ≠ ε ; as a consequence we have α ⇒ β implies |α| ≤ |β| CSG is a Noncontracting grammar. Formal