Within the continuous verbal forms the categorial meaning reveals the nature of development of the verbal action (the category of development). The marked member of the opposition here is the continuous, which is built up by the auxiliary be + the present participle of the conjugated verb (be...ing). The categorial meaning of the continuous is action in progress. The unmarked member of the opposition, the indefinite, leaves this meaning unspecified. This category is realized through the opposition Continuous vs. Non-Continuous (Progressive vs. Non-Progressive).
The perfect forms reflect in a relative way a kind of timing (the category of retrospective coordination). The marked member of the opposition is the perfect (the auxiliary have + the past participle of the conjugated verb: have ... en). This category is realized through the opposition Perfect vs. Imperfect/Non-perfect. Thus, the following forms should be distinguished: 1) perfect continuous and perfect indefinite, 2) imperfect continuous and imperfect indefinite.