Berkeley, partly in reaction to Locke, also attempted to reintroduce an "immaterialism" into early modern philosophy (later referred to as "subjective idealism" by others). He argued that individuals can only know sensations and ideas of objects, not abstractions such as "matter", and that ideas depend on perceiving minds for their very existence. This belief later became immortalized in the dictum, "esse est percipi" ("to be is to be perceived"). As in classical and medieval philosophy, Berkeley believed understanding had to be explained by divine intervention, and that all our ideas are put in our mind by God.