Such facts are endowed with a power of coercion, by reason of which they may control individual behaviors. According to Durkheim, these phenomena cannot be reduced to biological or psychological grounds. Social facts can be material (i.e. physical objects) or immaterial (i.e. meanings, sentiments, etc.). Though the latter cannot be seen or touched, they are external and coercive, thus becoming real and gaining "facticity". Physical objects, too, can represent both material and immaterial social facts. For example, a flag is a physical social fact that is often ingrained with various immaterial social facts (e.g. its meaning and importance).