Past and present participial adjectives can modify nouns and express completed or ongoing states. Past participles (-ed) express completed states and have adjective-like properties, while present participles (-ing) express ongoing qualities or states and have both adjective and verb properties. The document provides examples of participial modifiers and discusses tests to determine if they are functioning as adjectives or verbs in different contexts. It explores the differences between expressing a natural quality versus a resulting state depending on position before or after the noun.