The category of aspect is more abstract than actio verbi. They both form functional-semantic category of aspectuality as its central part. The primary stimulus of aspect formation is connected with the basic function of verbal aspect - to multiply the temporal-modal forms in aspect pairs. It is conjugation type of primary forms that is relevant for distribution of imperfectivization processes and forms. Primary forms are more frequent than secondary forms within aspect correlations. Aspect pairs represent 87 % of aspect correlations (1:1), nevertheless, there are also asymmetrical relations (1:2, 1:3, 1:4). Secondary imperfectives variants are influenced by grammatical, morphonological, diachronic and extralingual factors. Slovak National Corpus (SNK) serves as basis for the evidence of co-variants, co-existence of forms and ending of form which lost its function. This dynamics is reflected in the tension between codification, represented by lexicons, and language practice, represented by SNK. The important indicator of variants existence is represented by participles.