Although conventional keyword searches allow you to specify wildcards to capture word variations, many of these search results will likely contain words that are completely unrelated to the query.
For example, suppose that you enter the query reduce <AND> soap <AND> viscosity. This query automatically explores variations of tense, voice, and plurality of the query words, including reduces, reduced, soaps, and viscosities.
A keyword search automatically considers only those word variations that have the same meaning as the words in the query, and not simply the words that begin with a given character string (which can be irrelevant to your search).