Please read the updated version of this article: http://www.writemysite.co.uk/the-grammar-of-keywords/2015/10/08/
Defining your keywords is a critical moment in a site’s development and can make or break a your search engine optimisation efforts. A little knowledge of grammar and modifiers can help you to select the best keywords.
Different search engines treat plurals in different ways, so it’s always worth considering which form you are using. On Google, you can easily double your keyword hits by including both singular and plural forms of your keywords on the site. Google treats these forms as two individual words and brings up almost entirely different search results for each one. Consequently by optimising both forms you can theoretically achieve strong rankings in two independent searches.
The same does not apply to Yahoo, where singular and plural are treated as the same word. Using the different forms here will not damage your ranking, but you can’t double up in the same way as Google.
Using modifiers is another way to ensure your keywords are highly targeted: in SEO lingo this is referred to as creating ‘long tail keywords’. For example, there are possibly thousands of searches every day for ‘aquariums’, slightly less for ‘south England aquariums’ and even fewer for ‘Brighton aquariums’.
The targeted modifier ensures that you narrow the field of competition for high rankings and ensures that your web page is put in front of searchers who know exactly what they want, potentially increasing your conversion rate exponentially.