What are Presuppositions?
A presupposition is the condition or element in a statement which has to be true in order for the sentence to make sense. But in doing so we may accept something that is either true or false. It includes statements in which some unstated element must be assumed (pre-supposed) to be true in order for the statement to make sense (to be true or false). That is, the surface structure of the statements (the specific words and their meanings) omit or obscure the deep structure of the statements (their underlying message or presupposed truths). In the Meta Model, presupposition forms are named for the manner in which the sentences that contain them either delete or obscure them in the surface structure.
An advertisement that states, "We serve healthy low fat meals", presupposes that meals are served; that the meals are healthy according to someone's criteria and that low fat is healthful.
An advertisement for "low fat yogurt" presupposes that yogurt being low in fat has health benefits for some target group, and that regular fat yogurt could be bad for others. The image on the container will also have its own presuppositions that support the text. The placement of the yogurt container in the health section of the supermarket will contextually state the presupposition that low fat yogurt is healthy for health conscious people.
An advertisement in a health clinic, "Prevent your next heart attack.", presupposes that the reader has already experienced a heart attack and that they will have another unless they follow the instructions in the advertisement. Another medical advert read, "Prevent your next bone fracture."
An advertisement in a spam email had the heading, "Can this ten second trick prevent your heart attack?"