Is it necessary to use both singular and plural instances of a keyword?

Let say you sold umbrellas, would you need to list "umbrella" as a keyword if you already had "umbrellas" ?

Also, if a keyword is in a keyword phrase, is it necessary to list it by itself?
ie: "black umbrellas,umbrellas" ?

Thanks

 

Sorry, I didn't see a similar post when I put this up.

 

In a google search for 'umbrella' or 'umbrellas', you will find the same results. In that case, i would say no, it doesn't matter. But I never use too much of a single keyword. It is just not natural. Google knows which words are related and similar and I'd suggest to use keyterms in a group. Check out the Google keyword suggestion tool to see which words are similar to Google.

 

If I use a plural instead of a singular form of a keyword in key places such Load up both plural and singular on the same page,

 

doesnt matter