Whitehead pointed to the limitations of language as one of the main culprits in maintaining a materialistic way of thinking, and acknowledged that it may be difficult to ever wholly move past such ideas in everyday speech. After all, each moment of each person's life can hardly be given a different proper name, and it is easy and convenient to think of people and objects as remaining fundamentally the same things, rather than constantly keeping in mind that each thing is a different thing from what it was a moment ago. Yet the limitations of everyday living and everyday speech should not prevent people from realizing that "material substances" or "essences" are a convenient generalized description of a continuum of particular, concrete processes. No one questions that a ten-year-old person is quite different by the time he or she turns thirty years old, and in many ways is not the same person at all; Whitehead points out that it is not philosophically or ontologically sound to think that a person is the same from one second to the next.