Full Idea
If a brick and the song of a canary strike a window, which breaks....we can truly say that the song of the canary had nothing to do with it, that is, in so far as what occurred is viewed merely as a case of breakage of window.
Gist of Idea
When a brick and a canary-song hit a window, we ignore the canary if we are interested in the breakage
Source
Curt Ducasse (Nature and Observability of Causal Relations [1926], §5)
Book Reference
'Causation', ed/tr. Sosa,E. /Tooley,M. [OUP 1993], p.135
A Reaction
This is the germ of Davidson's view, that causation is entirely dependent on the mode of description, rather than being an actual feature of reality. If one was interested in the sound of the breakage, the canary would become relevant.