What makes a shoe more, or less, formal is defined by three major factors:
2. Surface Smoothness
3. Style Complexity
Each of these factors has about equal value, and can contradict each other in defining the formality of a shoe.
Let’s start with color first, since it is the most obvious at a glance. The formality of color holds true in both clothing and shoes. Black is the most formal and light browns the least formal. This is partly based on the old axiom that city colors are monochromatic while country colors are earth tone.
Shoe colors that fall outside black, brown and cordovan, such as greens or purples, are considered novelty colors in men’s shoes. The shade of the color also determines formality, with darker colors being more formal and lighter colors being less formal.
The next factor is surface smoothness. In this case we are talking about the leather material the shoe upper is made of. The smoother the leather surface the more formal, and the more texture the surface has the less formal.
Since patent leather is the smoothest leather it is the most formal. And, since suede has the most texture it is the least formal. The only exception to this rule would be shell cordovan, which is smoother than calf skin, but considered less formal than calf skin. Exotic skins like crocodile fall between cordovan and suede in formality.
It is important to note that fancy and formal are not the same thing. This is why some shoe novices think that a wingtip shoe is more formal than a cap toe shoe, which is simply not true. To explain why this is not true let’s look at the third factor which is style complexity.
The amount of decoration and/or seams on a shoe determines its formality. The less decoration and or seams the more formal the shoe. The more decoration or seams the less formal the shoe. Typically a cap toe shoe has less decoration and seams than a wingtip shoe (although not always).
Loafers, as a rule, are considered less formal than lace up shoes, with one main exception: The opera pump (also known as a court shoe). The opera pump is a whole-cut slipper made of black patent leather, with a short vamp (which defines it as a pump) decorated with a grosgrain bow. This shoe should only be worn with a tuxedo or true formal attire.
Other aspects of style complexity to consider is Oxford style (closed lace) versus Blucher style (open lace). Since the blucher style requires the quarters to overlap the vamp it adds more seams and complexity to the style, therefore causing the blucher style to be less formal than the oxford style.
Monk strap shoes are actually a style of blucher (although the monk strap existed before the term blucher was used), using a strap, rather than laces to pull the quarters closed over the tongue.
Clearly, all of the factors that define the formality of a shoe exist in every shoe in different and sometimes conflicting ways. For example a brown calf skin, wingtip, blucher would considered similar in formality to a black suede, cap toe, oxford; each having varying aspect levels of formality.