Fluid typographic forms (letters, numbers and other characters), which transform over time to present new identities, are employed in a new kind of temporal typography. These forms, and the behaviours they exhibit, are most commonly seen in temporal media, including television idents, credit sequences and typographic animation. However, fluidity is dependent upon characteristics that were developed historically, from the seventeenth to twentieth centuries. It has become possible to retrospectively identify the ways that historical developments anticipated fluid transformation in temporal typography. Some categories of fluid behaviour would be impossible if it were not for the concept of the letter as malleable, as a three-dimensional object, or as modular. These characteristics permit processes, or fluid behaviours, through which a new identity is introduced to a changing form. This article demonstrates that these three characteristics are reflected in three historical developments: the use of the transformable grid in the development of Romain du Roi, three-dimensional nineteenth-century typefaces and the modular lettering of Josef Albers, Theo van Doesburg and Bart van der Leck.