English Grammar Profile C1 point 80 in the category of PAST is defined as:
past simple ‘I thought’ as a politeness structure to sound less direct.
However, there is no way to formally decide if this is actually a politeness construction. If it is not, it might still contain B2 modal passive or B1 reporting structures.
For example:
We thought she would be killed.
If we follow the pattern of both the EGP examples:
I_P thought _PP _VM _VB
1 I THOUGHT IT WOULD BE 35535
I thought it would be a great opportunity to do a little experiment.
2 I THOUGHT IT MIGHT BE 8003
3 I THOUGHT I WOULD BE 2141
4 I THOUGHT THEY WOULD BE 1616
5 I THOUGHT IT ‘D BE 1600
6 I THOUGHT I ‘D BE 1130
7 I THOUGHT IT COULD BE 940
8 I THOUGHT YOU MIGHT BE 854
9 I THOUGHT I MIGHT BE 735
10 I THOUGHT IT MAY BE 646
11 I THOUGHT HE WOULD BE 510
12 I THOUGHT IT SHOULD BE 465
13 I THOUGHT IT MUST BE 384
14 I THOUGHT THEY ‘D BE 360
15 I THOUGHT THEY MIGHT BE 344
16 I THOUGHT YOU WOULD BE 264
17 I THOUGHT HE ‘D BE 259
18 I THOUGHT YOU ‘D BE 255
19 I THOUGHT WE WOULD BE 228
20 I THOUGHT HE MIGHT BE 222
21 I THOUGHT SHE WOULD BE 218
22 I THOUGHT I SHOULD BE 212
23 I THOUGHT I COULD BE 189
24 I THOUGHT WE ‘D BE 179
25 I THOUGHT IT WILL BE 124
26 I THOUGHT I MUST BE 118
27 I THOUGHT SHE MIGHT BE 110
28 I THOUGHT WE MIGHT BE 106
29 I THOUGHT YOU MAY BE 90
30 I THOUGHT THEY SHOULD BE 90
31 I THOUGHT SHE ‘D BE 81
32 I THOUGHT I MAY BE 80
33 I THOUGHT THEY MUST BE 65
34 I THOUGHT THEY COULD BE 61
35 I THOUGHT HE MUST BE 58
36 I THOUGHT HE COULD BE 58
37 I THOUGHT WE COULD BE 58
38 I THOUGHT THEY MAY BE 47
39 I THOUGHT YOU SHOULD BE 45
40 I THOUGHT WE SHOULD BE 44
41 I THOUGHT IT ‘LL BE 30
42 I THOUGHT SHE MUST BE 29
43 I THOUGHT HE SHOULD BE 29
44 I THOUGHT YOU MUST BE 23
45 I THOUGHT HE MAY BE 21
46 I THOUGHT YOU COULD BE 19
47 I THOUGHT I WILL BE 16
48 I THOUGHT SHE MAY BE 12
49 I THOUGHT IT CAN BE 11
50 I THOUGHT SHE COULD BE 11