While it is probably true that simple language structures are the easiest thing to teach and learn, we should look very carefully at what we consider to be simple.
Take for example English articles. There are only two of them: definite and indefinite — maybe three, if we count the allophonic variant of the indefinite article ‘an’. Unlike other languages, in English we don’t have to take into account gender or case when deciding which one to use. So, why are these items so difficult for English language learners? The answer to this question relates to the rules that govern articles, which are very complex, thus making their application somewhat difficult.