The computer does not think. It looks for exactly what you typed. If you misspell a word when searching on the web, you will get back pages where the word is also misspelled - not very reliable information.
Library catalogs have rules about words that can be used as subjects.
If searching on the web, try another search engine. Different search engines give different results. We recommend Google which has recently added an advanced search feature which allows for phrase searching and Boolean logic. If you find one good article, look at the subjects it was assigned in the database and use those for a new search. This technique works with many of our subscription databases - not on the free web.