Richard H. Smith, Ph.D., is a professor of psychology at the University of Kentucky who studies emotions in his article in psychology today he asks the question, "Is the Difference Between Envy and Jealousy?" It turns out that Psychologists agree on a fairly straightforward distinction.
Envy occurs when we lack a desired attribute enjoyed by another. Jealousy occurs when something we already possess (usually a special relationship) is threatened by a third person. And so envy is a two-person situation whereas jealousy is a three-person situation. Envy is a reaction to lacking something. Jealousy is a reaction to the threat of losing something (usually someone). This seems straightforward, so why the confusion?
One problem is an unfortunate semantic ambiguity with the word “jealousy” (but NOT with the word “envy”). If you ask people to describe a situation in which they felt jealous, they are as likely to describe an experience of envy (e.g., "I wished I had my friend's good looks") as of jealousy (e.g., "my girlfriend danced with an attractive guy"). Naturally, this creates a sense that jealousy and envy are very similar—even though they are actually quite different. The blend of jealousy and envy is a debilitating kick in the emotional solar plexus.
Therefore, when someone says, “I’m feeling jealous,” you don’t know whether he or she is experiencing an envy situation or a jealousy situation—unless more context is provided (e.g., “I felt jealous when I saw my girlfriend dancing with the attractive guy”).
The second problem is that envy and jealousy often travel together. What kind of rival to your partner’s affections is likely to create jealousy? It is the rival with characteristics that you are likely to envy—that is, the attractive rival. This means that when you are feeling jealous, you are often feeling envious as well.
And yet envy and jealousy are not the same emotions. Envy, as unpleasant as it can be, usually doesn’t contain a sense of betrayal and resultant outrage, for example. Jealousy need not contain an acute sense of inferiority (if the rival is not enviable).
When people take my course they are taught how to erase many of these negative feelings. Envy is just a short term motivator, but accomplishments beat envy every time.