I didn't quite understand your logic about natural vs not natural.

Quote Originally Posted by Yuki View Post
- Стол накрыт?
- Да, всё готово. Можно приглашать гостей.
Here usage of imperfective means that the speaker focus its attention on the process of invitating (progressive) rather than on the accomplished result. "You may go and start inviting guests." If the perfective is used it would mean something like "You can go and make guests invited."

Correspondingly in the previous example (1 - imperfective) can mean, for example, "I am in the mood to think of and propose ideas". (2 - perfective) can mean "I have several ideas and ready to make all of them proposed."

There can be other ways of treatment though.

So usage of imperfective in each situation can indicate that speaker thinks about the process of acting while perfective indicates that speaker thinks about obtaining the result of action. The choice between perfective and imperfective often is not clear for the foreigners because it is often the accepted way of thinking rather than strict formal rules. At first stage of learning language you can skip most part of the problem. Later intensive practice will give you intuitive feeling of what is more natural Russian way of thinking in what situation.