Soon after hearing the news that the Understanding Media project was to be funded, McLuhan wrote Harry Skornia in a May 29, 1959, letter describing his excitement about the task before them:

for the first time in history we are setting out to discover the patterns of subliminal action resulting from media — and since all of them are simultaneously operative in our midst today we can use the present as history, as lab for tests etc.

Just as present investigation in chemistry or genetics throws new light on what has happened in the past, so would exploration of media serve to illuminate human history. Study of possibility now can be applied to actuality then — “the present as history”.

Five years later, in another note to Skonia from July 6, 1964, he set out the obverse point: 

I only realized today that we cannot transcend our “flat earth” view of media so long as we rely on private impressions at a particular time and place. The meaning and effect of a medium is the sum total of all its impact upon psyche and society. Such a vision requires the historical dimension as the laboratory in which to observe to change. (…) By showing the effect of a medium upon a diversity of institutions, you gain the historical dimension of the present. (Letters, 305)

Just as present questions in chemistry can be suggested by historical events , so contemporary understanding of media can be prompted by past developments. Actuality then points to present possibility now — “the historical dimension of the present”.