ВОЙДИТЕ, ЧТОБЫ НАЧАТЬ ОБУЧЕНИЕ С АУДИО-ЗАПИСЬЮ

~ことにする - ~koto ni suru

 

ことにする - koto ni suru means "decide to do ...."
It follows the short form present tense of a verb. You can use a negated verb, too.

車を買うことにしました。 We have decided to buy a car.

kuruma-o kau koto-ni shimashita.

 
あの人がかわいそうだから、
あまり文句を言わないことにします。
I will not make too many complaints. I am feeling sorry for him already.
 

ano hito-ga kawaisoo dakara,
amari monku-o iwanai koto ni shimasu.

 
   
 

We sometimes use the volitional form of this construction, such as iku koto ni shiyoo,
instead of the simple volitional form of a verb, 行こう - ikoo, in suggesting an activity.
koto ni shiyoo has the additional implication that the suggestion is being made after a deliberation.

今年の夏はベトナムに行くことにしよう。 Let's take the plunge. Let's go to Vietnam this summer.

kotoshi-no natsu-wa betonamu-ni iku koto ni shiyoo.

 
   
  こと に して いる  - koto ni shite iru means "do something as a regular practice,"
that is, you have made up your mind that you should do something and have stuck to that determination.
毎日十一時に寝ることにしています。 I make it a rule to go to bed at eleven every night.

mainichi juu-ichi-ji ni neru koto ni shite imasu.

 
絶対にお酒を飲まないことにしています。 I have made this firm decision not to drink and have strictly followed it.

zettai-ni o-sake-o nomanai koto ni shite imasu.

 
   
~ことにする decide to do ... 
~ koto ni suru  
~ことにしている do ... as a regular practice
~ koto ni shite iru