Structure and Form
Each type has a certain structure or way it is built. We are already aware of this since we categorize type into six categories. They each have characteristics that make them similar to other type faces that fall into that same category (Williams). The way to draw attention or add contrast using structure, is to use two type faces of different structure. Another words, from two different categories(3). Simply increasing size and/or weight(1) is not always as effective as using two types of different structure(2).
Form is closely associated with structure but refers to the type's shape. Sometimes the shape of letters in one type are very similar to those of another typeface, such as the flowing form of type that looks handwritten(4). Once again, make use of two different forms(5). This makes the text more distinguishable and appealing.