Full Idea
How can there be a science of a Heraclitean flux of acts of consciousness? Husserl answers that this is possible only if these acts are described in respect of their invariant or essential structure. This is an 'eidetic' scence of 'pure' psychology.
Gist of Idea
There can only be a science of fluctuating consciousness if it focuses on stable essences
Source
report of Edmund Husserl (Ideas: intro to pure phenomenology [1913]) by Rudolf Bernet - Husserl p.199
Book Reference
'A Companion to Continental Philosophy', ed/tr. Critchley,S/Schroeder,W [Blackwell 1999], p.199
A Reaction
This is his phenomenology in 1913, which Bernet describes as 'static'. Husserl later introduced time with his 'genetic' version of phenomenology, looking at the sources of experience (and then at history). Essentialism seems to be intuitive.