Final answer:
Periphrasis involves using a longer, indirect way of saying something, while inflection involves altering the form of words to express grammatical relationships. Descriptive language includes tools to enhance vividness, and subject-verb agreement is a grammatical rule ensuring verbs align in number with their subjects.
Step-by-step explanation:
The concepts of periphrasis and inflection concern the ways in which language expresses relationships between words and additional meaning beyond the literal. Periphrasis refers to the use of a longer phrase to express what could otherwise be conveyed with a shorter form or a single word. It is a roundabout way of speaking or writing. For instance, using 'a person of great wisdom' instead of the single word 'wise'. In contrast, inflection relates to the modification of words, particularly nouns and verbs, to express grammatical relationships such as tense, case, voice, aspect, person, number, gender, and mood. An example of inflection is changing the verb 'walk' to 'walked' to indicate past tense or 'walks' for third person singular present tense.
Concerning descriptive language, it encompasses the use of adjectives, adverbs, and other linguistic tools to add vividness or emotional intensity to language. Figures of speech, such as metaphors and similes, are forms of descriptive language that draw comparisons to add richness and layers of meaning to text. An example is the simile 'Learning a foreign language is like learning to ride a bicycle'. Meanwhile, subject-verb agreement is a grammatical rule that states the subject must agree in number with its verb. A single subject takes a singular verb, while a plural subject takes a plural verb.