Escape hatch

Escape hatch is a term referring to the fact that elements in COMP do not have to obey the Tensed-S Condition (TSC) and Specified Subject Condition (SSC) when moving to the next higher COMP. Thus, COMP functions as an escape hatch for movement. This is evident from the following joint definition of TSC and SSC:

No rule can invoke X,Y in the structure ...X...[a...Z...-WYV...]..., where (a) Z is the specified subject of WYV or (b) Y is in COMP and X is not in COMP or (c) Y is not in COMP and a is a tensed S

The reduction of TSC and SSC to Binding Theory and the introduction of barriers to define cyclic nodes has made this stipulation superfluous. In the barriers-framework, VP-adjunction can create escape hatches.

Link
Utrecht Lexicon of Linguistics