In this article, I tried to find out the reason why давно and долго, which have distinct definitions in russian academic dictionaries, are so often confused in their usages and seem to be understood as semantically very closely related lexical items. Furthermore in many contexts they seem to be interchangeable without any damages in meanings. Traditionally, russian academic dictionaries divided the meanings of давно into давно1 and давно2. They are different, in principle, in that the former is based on retrospective perspective, while the latter is on prospective perspective. For давно1, a new situation followed after the former event was finished, and the result or effect of the new situation has been continued to the present, as speech point, while for давно2, the event itself has been continued to the speech time. In both cases, the new situation for давно1 and the event for давно2 share the common factor < remotedness from the present as a speech point >. For давно, two points, a reference point and speech points are essential, and even a reference point in the future, is allowed with a help of context. However, for долго, setting the reference point is not essential because all the focus is primarily on the continuity of the event itself, and the duration of the event is unmarked with regard to the reference point.
Давно, including давно1 and давно 2, is sensitive to the relationship between the present as a speech time and the event time that is perceived to be located so far away in the past by the speaker, so can be referred as deictic while долго is non-deictic in that it focuses only on the structural characteristics of the event itself. These differences in semantic structure between them can be renamed as the tense-oriented давно and the aspect-oriented долго. And lastly, the divergent nature of уже are well combined давно, which presuppose the maximum distance and remotedness of the events or situations from the present as the speech time, while the convergent nature of ещё is well combined with долго, which asserts that the event lasts for a considerably long time within a certain closed time interval.