They indicate an assumption based on our knowledge of people and things, their routine, character and qualities.
WILL and WON'T are also used to express what we believe or guess to be true about the present. His latest book will be out next month.The truth or certainty of what is asserted is more or less taken for granted. WILL and WON'T are used to predict a future event or action which are seen as certain. Modal Verbs expressing certainty, probability or possibility
But they can also express ideas such as willingness and ability, permission and refusal, obiligation and prohibition, suggestion, necessity, promise and intention. All of them (except for NEED) can express degress of certainty, probability or possibility of an event.
