Morphology is the study of the structure of words and morphemes. Morphemes are the smallest units of meaning and cannot be broken down further. There are two types of morphemes: free morphemes which can stand alone as words, and bound morphemes which must be attached to other morphemes and cannot stand alone. Inflectional morphology deals with changes in word forms to express things like number, tense, or comparison. Derivational morphology involves using affixes to derive new words that may be a different part of speech than the base word.