Both words refer to growing or becoming greater. To increase is to grow in number, size, strength, or quality. It implies the simple fact of something becoming greater as opposed to shrinking or staying the same: The population increased by 2 percent. Escalate, which derives from escalator, an invention in use by the 1920s, suggests a steeper, sometimes alarming increase in intensity or magnitude, sometimes in prices, but more often in tense situations. If a situation, confrontation, or conflict escalates, it begins to get out of hand or threatens to escalate into something full-blown.