The first key in understanding copyright law is defining what it is these laws protect. Creative work is defined as being a production based on the thoughts, expressions, or imagination of an individual which developed with a physical existing form.
Simple thoughts held in a persons' mind are not creative works. However, they make take the form of creative works when developed through writing, art, etc. There is also a form which inhibits creative editing or collecting of work which allows the creative organization of the facts to be copyrighted. This is called a compilation copyright. In some areas it has specific guidelines. In any case, knowing the laws of creativity is beneficial.
The purpose of these copyright laws is to offer the creator exclusive rights and control over who may copy their work or compose variations involving their work. These laws provide these creators with secure protection and initiate penalties for those who violate the creators rights. It also gives the creator the ability to sell or license their work.
Most often, copyright has to do with commerce. Commerce involves the social relations involved in trade or exchange of goods and services. To be enforced it's logical that creative works should have some commercial value. Which means its not only suitable for a large market but gives quality to the particular market it's associated with. As an example, brainstorming would not be significant to copyright protection and of course has little or no value to anyone other than the person it developed from. However, what is developed from the brainstorming may be seen by others as valuable.
Something as simple as your opinion can be seen as valuable if it is documented physically and in creative form. While copyright violations aren't carried over into e-mail and forum postings caution is still needed in places such as USENET and others on the web. These places are huge and considered to be 100 percent publication.
There are some complexities in copyright law which allow certain types of copying without given permission to which it is felt that important social principles would possibly be violated. This is often associated with the concept of review or illustration of a particular point. Most major nations uphold the Berne copyright convention which states that the moment a work is created in a physical form, it's copyrighted. There is no legal notification necessary and it's not necessary to register. However, in the event of legal action, registration is often required.
Copyright continues seventy years after its creator is deceased. Copyright is a matter of common decency and respect. Taking something which doesn't belong to you without permission is theft and considered punishable by law.