We often speak of linguistic forms as ordered from left to right rather than from earlier to later, as though linguistic units exist only as displayed on a page and not as if they precede and follow each other in time as they are produced, understood, or structured.
An abstract feature of time, namely linearity, has always been implicitly necessary in linguistic structures. A number of abstract features of space-time, here collectively referred to as multi-linearity, are also fundamental to linguistic representations at the level of (so-called) ``non-linear'' phonology. Only partly formalized in non-linear phonological theory, these abstract features of space and time are here made explicit with reference to linguistic structure. Additionally, three fundamental and otherwise unrelated principles of non-linear phonological theory (the Well-Formedness Condition(s)) are proven to follow from them.