The presumption of validity refers to the fact that, once a patent has been issued, the courts will presume that it is valid, unless there is evidence to the contrary.
Section 43(2) of the Patent Act[1] creates the presumption of validity: In Diversified Products Corp v Tye-Sil Corp, the Federal Court of Appeal held that the presumption of validity merely gives rise to an evidential burden on a balance of probabilities.