This principle has been a foundational insight for theories of syntax since that time.
1	This	this	DET	DT	Number=Sing|PronType=Dem	2	det	2:det	Discourse=evaluation-comment:33->29:3|Entity=(65-abstract-giv:act-cf1*-2-coref
2	principle	principle	NOUN	NN	Number=Sing	7	nsubj	7:nsubj	Entity=65)
3	has	have	AUX	VBZ	Mood=Ind|Number=Sing|Person=3|Tense=Pres|VerbForm=Fin	7	aux	7:aux	_
4	been	be	AUX	VBN	Tense=Past|VerbForm=Part	7	cop	7:cop	_
5	a	a	DET	DT	Definite=Ind|PronType=Art	7	det	7:det	Entity=(65-abstract-giv:act-cf1*-3-pred
6	foundational	foundational	ADJ	JJ	Degree=Pos	7	amod	7:amod	_
7	insight	insight	NOUN	NN	Number=Sing	0	root	0:root	_
8	for	for	ADP	IN	_	9	case	9:case	_
9	theories	theory	NOUN	NNS	Number=Plur	7	nmod	7:nmod:for	Entity=(70-abstract-new-cf4-1-sgl
10	of	of	ADP	IN	_	11	case	11:case	_
11	syntax	syntax	NOUN	NN	Number=Sing	9	nmod	9:nmod:of	Entity=(25-abstract-giv:inact-cf3-1-coref)70)
12	since	since	ADP	IN	_	14	case	14:case	_
13	that	that	DET	DT	Number=Sing|PronType=Dem	14	det	14:det	Entity=(60-time-giv:inact-cf2-2-coref|XML=<date notBefore:::"1963">
14	time	time	NOUN	NN	Number=Sing	7	obl	7:obl:since	Entity=60)65)|SpaceAfter=No|XML=</date>
15	.	.	PUNCT	.	_	7	punct	7:punct	_
