Page 557 - Makino,Tsutusi.DictionaryOfIntermediateJGrammar

to iu koto wa 483
[Related Expression]
Koto also changes a sentence into a noun clause. The difference between S
to iu koto and S koto is that the former is used when S represents a concept
rather than a fact (e.g., KS(A)) or when the speaker / writer views the con-
crete content of S at a conceptual level (e.g., KS(B) and (C)). On the other
hand, S koto is used when S represents a fact (or something nearly factual)
and the speaker / writer views it at a concrete level. The following examples
illustrate this point.
First, S koto cannot be used when S is unlikely to happen. In this case, S to
iu koto is used, as in [I].

Second, if S represents a fact which the speaker/writer knows through
his 1 her direct experience, only S koto is acceptable, as in [2].
[2] @Pf 0%3 9 G:?+?27P37': I@/??tL\j] Ztb3.$&l?,
(It is a fact that he didn't come to the meeting.)

However, if S represents a fact which the speaker / writer knows through
indirect experience (i.e., through secondhand information), S to iu koto is
acceptable, as in [3].
[3] @@&%LI: {0/2~\31 ZtbiS$U&
(It is a fact that he got divorced.)

Third, if S represents something likely to happen, both S koto and S to iu
koto are acceptable, as in [4]. In this case the speaker 1 writer may view the
situation at either a concrete level or a conceptual level.

Fourth, when verbs like kanjiru 'feel' and y6kyijsuru 'request; demand' are