Distinguishing between necessity as a need and necessity as a modality, Aristotle’s simple definition of logical necessity is offered as “that which could not be otherwise”. This notion of ‘strict’ necessity is posited as a primitive concept, i.e. as a basic concept under which no other concepts are found. As such, it is discussed as an inborn notion, a constitutive feature of human rational thought, and not a metaphysical feature of the world. Logical necessity is shown to be cut from the same cloth as logical impossibility. Logical impossibility is defined as “not-possible” and logical necessity is defined as “not-possible not”, which is still a “not-possible” as opposed to a “possible”. Thus, ‘not-possible’ is shown to mean both “impossible” and “necessary”. Varieties of necessity, other than logical, are discussed and dismissed.