Learning the proper use of articles is one of the most complicated aspects of the English language for non-native English speaking scientists. Some languages, such as Chinese, Japanese, Polish, and Russian, have no articles. Arabic has only the definite article, and article use varies in German, French, and Spanish. For example, in German, articles are used differently based on the number, gender, and case of the nouns to which they refer. In English, articles are not always necessary, whereas in French and Spanish articles are used for almost every noun and, as in German, agree in gender and number with the noun with which they are used.