Cannot

Spell the negative as one word unless the not belongs to a separate phrase (e.g., not only . . . but also), though this exception is rare and usually worth rephrasing. While grammatically passable, He can not only be hot but also be shivering reads more cleanly when written as He can be not only hot but also shivering. The negative’s incorrect variant, can not, while more common than the above exception, is still, thankfully, rare.