SEO vs. advertising

Could you see the difference between SEO and advertising. They have something in common, and that is to promote their site, products and services. But I know there's a difference vetween thse two, since they have common things to do. SEO is a term in which you build backlinks to your site either on content, web directories, social bookmarks, relevant links and etc.

On the other hand, advertising is a way to promote your product, site or services with some sales letter or content related to classified ad posting like Craigslist. But guess what, advertising can be SEO, because they also generate backlinks but only on a temporary basis, while SEO assures that the backlinks are already permanent, depending on the admin of the sites if he's strict or not. So we know now how SEO and advertising are differentiated.