This article represents a crytical analysis of the ideas layed down within the framework of the complex natural morphology theory which examines the problem of system correlation of morphological naturalness viewed as normality and regularity of the morphological paradigms. Special consideration is given to the presence of suppletivity in the morphological paradigm of the flective languages and its preservation in the language system regardless of fact that according to naturality criteria deduced by the natural morphology school it should be defined as completely non-natural occurance and thus drop out of the language system. The suppletivity does not dissapear in the flective morphological languages – what is more, it reproduces itself where there are certain circumstances for its dissapearance under the influence of non-morphological agents.The reasons why it does so are still being examined.