Quote Originally Posted by Звездочёт View Post
Я могу объяснить, что имел в виду, когда писал первое сообщение, и когда писал второе. Вот только я боюсь, что мы зафлудим тему офтопиком. Я и раньше слышал, что очень трудно объяснить иностранцу склонение по падежам, используя систему вопросов, которой нас обучают в школе. Думаю, Вы правы: подобными объяснениями лучше не злоупотреблять. Но иногда очень хочется показать структуру предложения, взаимосвязь его частей. Ума не приложу, как это сделать, не прибегая к помощи падежных вопросов.
I understand what you mean even without your clarifications that might, as you said, flood this topic. The thing is I think you're mixing up apple and oranges here. This is what caused this lengthy and, I'm pleased to say, civil argument. But back to the apple and oranges.

I firmly believe that conjugation questions are very deceptive. A native speaker might easily fall to the feeling that they're a perfect tool to express how different parts of a sentence interact with each other. But they're not, they're just shortcuts to constructs you, as a native speaker, heard and repeated thousands upon thousands times in your live.

писать (чем? )ручкой/угольком/пером... and any other possible word that will make sense in conjuction with писать, granted you put it in the instrumental case. But let's think about what чем is. Чем is nothing more than the word что conjugated into instrumental. As you can see there is a pattern here that strongly points at this:

Use instrumental after the verb писать when you want to say that you write using the thing the conjugated word means as a tool.

You can do the trick with any other Russian case. The conjugation questions are just indicative of a pattern and you, as a native speaker, has encountered such patterns throughout your life, you have a lot of experience with them, that's why they make so much sense to you.

But anyone devoid of this experience will never put 2 and 2 together here. That's why they need help building their experiece with the patterns of the Russian language. We need to explain them to learners.

But you don't explain a pattern with a pattern for obvious reasons. But you might just achieve that by explaining what the reason we use this pattern in a particular situation is.