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2.2. The Classification of Functional Styles
The English literary language has evolved (*developed gradually by a long and continuous progress) a number of FSs easily distinguishable one from another. They are not homogeneous and fall into several variants. The classification of FSs is one of the most disputable and difficult problems in Stylistics. The reasons for it are as follows:

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  FSs are historically changeable categories;
  
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  The boundary lines between FSs are not clearly cut;
  
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  The criteria of classification of FSs have not been defined yet.
  

Each FS is a relatively stable system at given stage in the language development, but it changes in the course of time, and sometimes considerably. The development of each style is predetermined by:

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  the changes in the norms of Standard English;
  
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  the changes of social conditions;
  
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  the progress of science and the development of cultural life in the country.
  

The boundary lines between FSs are rather vague, because some FSs have common features. For example, the oratory style has much in common with the publicistic style; while the latter has many similar features with the scientific prose style. Up to now the criteria of FS classification remains disputable. The majority of linguists speak about five FSs: the belles-lettres style, embracing all genres of emotive prose; the style of official documents; the scientific prose style; the publicistic style; the newspaper style.