There are there levels of adjective in English. The base form is when we are describing only one object, we say or write the very raw form of the adjective. (i.e. pretty). Next, we have the comparative form wherein we add -er to the end of the adjective to compare two objective, (i.e. prettier). Lastly, we have the superlative, wherein we add -est to say prettiest when we describe three or more objects.