Has or have?

[amble007]

Should I use "has" or "have" in the following sentence? ---- "We added all of the suggested literature, which has strengthened ..." Thanks for help!

 

[probus]

"Which" refers to the whole of the clause that precedes it. Therefore you should use "has". You can remember this by imagining a "fact" after has: "We added all of the suggested literature, which fact has strengthened ..." Don't use the word fact, just imagine it.

 

[amble007]

Ok. That makes sense.

In some other situations (not with "which" but other words), it will depend on what it actually refers to (single or plural). This is why I am confused.