Consistency, from the latin cohaerentĭa, is cohesion or the link between one thing and another. The concept is used to discuss all that is logical and consistent compared to what precedes.
Examples: "the Secretary has shown consistency requesting his resignation until his boss the licensee", "what you say is not consistent", "president has said that he will continue to work consistently to resolve the problems of the population.
Consistency, it is therefore to be constant, faithful to its principles and keep the same position since the beginning. If a man says that it would be unable to leave his country and decided to settle abroad, after a few weeks, its behavior is inconsistent (noncoherent). On the other hand, if a soccer player said that he would never play in another club than his own and that he rejected a millionaire offer from another team, arguably there is a consistent person.
Consistency is also associated with which is understandable from the point of view of logic. A politician has a coherent discourse if it does not empty promises or if it does not distort the reality. On the other hand, it would be inconsistent if he promises things he could never keep.
For Linguistics, textual coherence is the State of a text in which components Act in solidarity groups. This means that, beyond the unitary authorities and secondary ideas, it is possible to find a global sense around a main theme.
Words, sentences and paragraphs are coherent insofar as they create the sense of a chapter, while chapters are consistent for the unit of a book.