This article on cantusmodalis.org requires a little effort, like all valuable things. It begins with…
In its most general context the word modus or ‘mode’ may be defined as ‘a manner or way of acting, doing or being’. In this definition the emphasis is placed on the process of being or of moving toward a certain something which in itself, although constituting the sole reason for the process, can only be the passive result of the way the process itself unfolds.
…and concludes with this gem of a sentence:
In fact chant exists because of the enormous force of attraction of an end which is not an end but a transformation into that which will remain forever beyond us.
I recommend using a pencil when you do, but please, consider reading:
Follow-up post : Reality of rhythmic movement – Nature of vocal movement.
Read more on “modality”: Modality – introduction