In contrast to nouns, little is known about the graded structure of adjective categories. In this study we investigate if adjectives categories show a similar graded structure and explain it using a similarity-based account. The results show a reliable graded structure which is adequately explained by two formal models based on prototypes and exemplars, therefore generalizing the model performance from concrete nouns to adjectives. Finally, we show the attention weights of these models deal with the additional challenge of antonymy in adjectives and discuss the findings in the light of alternative accounts that do not rely on item-similarity.