Cohesive devices are linguistic elements like pronouns, conjunctions, and lexical reiteration that link different parts of text together at the semantic level. The major functions of cohesion are to help form a unified text and achieve coherence. There are various types of cohesive devices including reference, substitution, ellipsis, conjunctions, and lexical items. Examples like pronouns, demonstratives, and comparatives can create reference, while substitution replaces linguistic items and ellipsis omits words. Conjunctions join words and sentences, and lexical cohesion uses reiteration and collocation of words. Cohesive devices are important for creating meaningful text and improving reading comprehension.