Could anyone possibly tell me what the differences of the two words are? Or, when can't we use them interchangably? Thanks a lot in advance...
Develop is basically to change something for better, bigger, stronger or more advanced while Improve is to add or remedy a deficiency/a felt need to make something better by advancing to a more desirable, valuable, or excellent state.
They are not synonyms but can be interchangeable when a betterment is achieved either through an act of change or an act of remedying the deficiency. Such as: SKILL/ABILITY The course is designed to help students develop/improve their speaking skills. You must develop/improve analytical ability to critically review the literature
Think of a seed - it develops into a plant/flower/vegetable. There was nothing wrong with the seed - it just needed to grow.
Think of a piece of desert land, and then I build an apartment building there. I have developed the site - made it more than it was before.
Now - think about the old cathode ray TVs, and then the new flat screen LCD TVs. They are an improvement in TVs because, for one thing, they take up less space. There was a 'fault', or a way in which something that already existed could be made even better.
So - the desert land did not have any buildings on it - it had to be change into something else that was 'useful'. It needed development, whether as a site for housing, or as farm land.
With the TVs, something existed, and was made even better...just as LCD TVs are being improved and in a few years we will have with LED TVs.