SN4 ""

No	Pattern	Freq
1	[conj] [pers pn] could have been [adj]	33
2	[coord] [pers pn] could have been [adj]	19
3	[verb] [pers pn] could have been [adj]	18
4	but [pers pn] could have been [adj]	13
5	but [pers pn] could have been [adj]	13
6	[noun] [pers pn] could have been [adj]	10
7	[noun sg] [pers pn] could have been [adj]	9
8	[adv] [pers pn] could have been [adj]	8
9	that [pers pn] could have been [adj]	7
10	that [pers pn] could have been [adj]	7
11	[that] [pers pn] could have been [adj]	7
12	[subord] [pers pn] could have been [adj]	7
13	[vb base] [pers pn] could have been [adj]	7
14	[adv] [pers pn] could have been [adj]	6
15	if [pers pn] could have been [adj]	5
16	[vb past] [pers pn] could have been [adj]	5
17	if [pers pn] could have been [adj]	5
18	and [pers pn] could have been [adj]	5
19	and [pers pn] could have been [adj]	5
20	[pers pn] could [adv] have been [adj]	62
21	[pers pn] could not have been [adj]	46
22	[pers pn] could [not/n't] have been [adj]	46
23	[pers pn] could n't have been [adj]	26
24	[pers pn] could not have been [adj]	20
25	[pers pn] could [adv] have been [adj]	16
26	[pers pn] could have been [art] [adj]	50
27	[pers pn] could have been [art] [adj]	50
28	[pers pn] could have been [adv] [adj]	35
29	[pers pn] could have been a [adj]	35
30	[pers pn] could have been [adv] [adj]	35