Back in third grade, I first learned about set theory and Venn Diagrams.  I have to admit that I never foresaw a career where I tend to draw Venn diagrams several times a day!  Let’s let the left circle represent all the records in a database that contain the word “mathematics.”  The circle on the right represents the set of all records that contain the word “fear.”  Thanks to people like me that struggled mightily with multiplying and dividing fractions (at first) in fifth grade, we can expect that educators have looked into the problem of kids being a bit afraid of math.  The green shaded area represents records that contain both words.  The circles aren’t drawn to scale of course.  The set of records with the word “mathematics” was much larger … more than ten times larger.  Hopefully this makes the search more understandable.  One thing that you should realize is that the result of using an AND Operator should be a set of records that is SMALLER than either of the two sets that you started with (it could be the same size as the smaller of the two sets … but that is not likely to happen).  It’s important to note that using too many AND Operators may yield sets that are too small to cover the topic.  Start with the most significant concepts for your search and combine them until you have a reasonably sized set to work with.  Don’t overuse the AND Operator.  Use it, but do so wisely.  Think about the topic and the impact that your strategy might have on your results.