Boolean search utilizes AND, OR & " " to narrow results. Concept search is what we call a "smart" search, where it will search for what you might mean. It does this by searching synonyms, alternate tense, etc. Pattern search should be used when you're unsure of the spelling of the keyword (i.e. if you want to search the word 'thief', but can't remember if 'i' comes before 'e', it would be best to use this search).