The phrase "evidentiary foundation" refers to the factual proof or support that is necessary to establish or validate a claim or argument. It means having enough reliable evidence to substantiate or back up a statement or position. Full definition
The appellate court affirmed, agreeing that the public entity had to lay a much more detailed evidentiary foundation for a section 1038 showing rather than having the trial judge «work up the motion» for the City. (calattorneysfees.com)
[64] It is, therefore, a misapplication of the «robust and pragmatic» approach to make a finding or draw an inference of causation where no factors of the kind set out in Snell are present and the proper evidentiary foundation is absent. (slaw.ca)
The question of whether the quantum paid by IPEX was justified or reasonable required a full evidentiary foundation at trial. (blg.com)