What is cohesion in writing?

Cohesion is the “glue” between your sentences. It comes from linking words (however, as a result, for example), pronouns that point clearly back to what they replace, and putting ideas in an order that flows. Good cohesion means a reader moves through your writing without ever stopping to work out how one sentence relates to the last.

It is closely tied to coherence: cohesion is the sentence-to-sentence connection, while coherence is whether the whole piece makes sense as one argument.