Demonstrate means to show clearly how something works or why something is true. When your teacher demonstrates a science experiment, she performs it step-by-step so everyone can see exactly what happens. When a coach demonstrates the proper way to swing a bat, he shows you the technique by doing it himself.

The word also means to prove something through evidence or examples. A student might demonstrate her understanding of fractions by solving problems correctly. A city's rising crime rate might demonstrate that its police force needs more resources. Scientists demonstrate their theories through careful experiments that anyone can repeat and verify.

In another context, to demonstrate means to participate in a public protest or rally, usually to show support for or opposition to something. People might demonstrate for better schools or against an unfair law. These public gatherings are called demonstrations.

Notice that demonstrating always involves making something visible or obvious to others. You can't demonstrate something privately in your head. Whether you're demonstrating how to tie a knot, demonstrating your soccer skills, or demonstrating your opinion by marching with a sign, you're making something clear through actions that others can observe.