 ‘Natural deduction’ also designates the type of reasoning that these logical systems embody, and it is the intuition of very many writers on the notion of meaning—meaning generally, but including in particular the meaning of the connectives behind active reasoning—is based on the claim that meaning is defined by use. Much has been written in this area that categorizes some important aspects of formal logic as manifesting this feature also, and in particular that it is most clearly at the fore in natural deduction.