Read the "How do We Classify Matter?" section. All matter can be classified as either a pure substance or a mixture. Furthermore, for a pure substance, a subcategory of either single-element or compound can be applied. Mixtures are further categorized as either homogeneous (single-phase) or heterogeneous (multiple phases). The distinction between homogeneous and heterogeneous mixtures presented here is dependent on phase, or physical, boundaries. This section also contains material relevant to the next section of the course.