A shift is an abrupt change of some sort that results in inconsistency. Sometimes writers and speakers create deliberate shifts, as linguist Geneva Smitherman does in this passage from Word from the Mother: “In the larger realm of Hip Hop culture, there is cause for optimism as we witness Hip Hop younguns tryna git they political activist game togetha.”
Unintentional shifts, however, can be jolting and confusing to readers.