Is the notion of planting evidence also so colloquial that what’s planted is not evidence?
If it is planted, then no, it can not be evidence. It is--once again--someone
mistaking something to be evidence when in fact it is not. This is not a proposition from Wittgenstein.
"Evidence" is conditional. A gum wrapper in and of itself is not evidence
unless the gum wrapper can be tied directly to a crime (i.e., it has the suspect's DNA on it).
No police officer picks up a gum wrapper and says, "Ah ha! This is evidence in the sense that it's been concluded to be evidence of a crime!" They would only at best consider it
potential evidence until it has been thoroughly examined, but again, that's semantics. It doesn't become substantive until such time as the investigation of it is complete and concrete conclusions can be drawn.
Iow, the determination that something is evidence of a crime (or evidence of an assertion; or evidence of a truth claim) is whether or not that something can be substantively tied to the conditions of the crime (or assertion or truth claim). Hence the question,
does the evidence support the assertion?
If it doesn't, then there is no point is labeling it "evidence" (strong or weak). It's just
not evidence. It's a gum wrapper.