One of the ways adjectives can be categorized is to determine whether they are coordinate or noncoordinate adjectives. This distinction is important, because it dictates whether two or more consecutive adjectives are separated by punctuation. For many writers, however, deciding which category an adjective belongs to can be a challenge. Fortunately, two simple tests are available to help writers know how to treat strings of adjectives.
First, if two or more adjectives are separated by commas, can and substitute for each comma? Because each of the three adjectives in the sentence “The pale, gaunt, sepulchral figure seemed to float above the floor” independently describe the figure, the sentence can be revised to read “The pale and gaunt and sepulchral figure seemed to float above the floor.” And though English observes a natural sequence of types of descriptive words called the royal order of adjectives, these words are all visually descriptive, so the sequence can be reversed without affecting comprehension: “The sepulchral, gaunt, and pale figure seemed to float above the floor.” These adjectives are coordinate, and they should be separated by commas.
However, in the sentence “Her thin green cashmere sweater did little to keep her from shivering,” each adjective builds on the next: “cashmere sweater,” “green cashmere sweater,” “thin green cashmere sweater.” In addition, one would not write, “Her cashmere green thin sweater did little to keep her from shivering,” because that sequence violates the royal order of adjectives. Therefore, the adjectives are noncoordinate, and no punctuation should intervene.
Use these tests to determine which of the following sentences include coordinate adjectives and which contain noncoordinate adjectives:
1. The object is a small, platinum and iridium cylinder weighing exactly one kilogram.
Small describes the nature of a cylinder made of platinum and iridium, so that word is not equivalent to the other adjectives, nor would the sentence be written, “The object is a platinum and iridium small cylinder weighing exactly one kilogram”: “The object is a small platinum and iridium cylinder weighing exactly one kilogram.”
2. Uber has been dogged by controversy on the road to becoming one of the most valuable, privately funded companies in the world.
The modifiers “valuable” and “privately funded” are not equivalent—one would not write that the company is “valuable and privately funded” or that it is “privately funded and valuable.” A privately funded company is being described as one of the most valuable such companies in the world, so no punctuation should intervene between the adjective valuable and the descriptive phrase “privately funded companies”: “Uber has been dogged by controversy on the road to becoming one of the most valuable privately funded companies in the world.”
3. The battered, clanking, smoking vehicle lumbered along the road.
The three adjectives preceding vehicle are all sensory and are thus coordinate, so punctuation is correctly employed in this sentence: “The battered, clanking, smoking vehicle lumbered along the road.”