Page 447 - Makino,Tsutusi.DictionaryOfIntermediateJGrammar

sai (ni) 373
5. N ni saishite is more formal than N no sai ni. When the former is used,
N has to express a very special occasion as in KS(C) and Ex.(g). If N
expresses an occasion which is not so special as in Ex.(e), N no sai ni
cannot be replaced by N ni saishite.

e elated Expressions]

I. Sai ni indicates the time when s.t. special takes place,whereas on ni
indicates an occasion when s.t. ordinary takes place.
SL? k %V
I)J~/*KI
[I] a. H~Fc=L~L;~L+~ C=~~Z$&&T;SL~,
(If you have a chance to come to Kyoto, please let me
know.)
$L * .
bi? A
/
{B&
b. ~~~ii%%?!&F& *)Jil $JDWTQ&TL~Q~.~~:,
(When Bill got married he hadn't obtained his parents' per-
mission.)
For the difference between toki ni and sai ni, see Note 1 above.
(+ toki (DBJG: 49044))
11. There is another expression ba'ai, 'case,' which is used in the form of
Vinf ba'ai or N no ba'ai.

b. %PF& / e / *RI din4 + 7 TCP$ZT-F~
7:
(If it rains the hiking will be cancelled.)
c. AKD {a+/ @ / EI car~.-;-~-~T&bi~b~.a~~s

LAO
(In case of fire please don't use the elevator.)
Ba'ai means 'a suppositional case,' so an event that precedes it may not
take place. So if the event is a real event, ba'ai cannot be used.