Coherence (ittisaq al-kalam) means more than uninterrupted words: the denial and affirmation must form a valid corrective relation. The textbook discusses a historical marriage-contract illustration involving different dower amounts.
«لا أجيز النكاح بمائة درهم، لكن أجيزه بمائة وخمسين درهما»
I do not approve the marriage at a hundred dirhams, but approve it at a hundred and fifty.
The source treats that particular contract as invalid because the statements are not coherent: the first proposed transaction has been rejected and the subsequent wording does not operate as a valid connected correction. This is not a universal ruling that all revised dower proposals are invalid.
Review: Waw — simple conjunction; fa — connected succession; thumma — delay; bal — correction; lakin — qualification after denial. Always ask whether the primary sense operates or context supplies a recognized secondary meaning. Next: aw, hatta and other particles.