Whereas other philosophical schools like the Confucians posited a stable natural order (e.g. heaven and earth), the Mohists never arrived at such general principles.
They could only debate the meanings of words (ming) and their relation to reality.
The Mohists were very practical, and so stayed away from abstract or metaphysical topics of study, instead focusing on specific meanings for words.
The Mohists thus focused on the observable everyday world and its correlates in words.