In a proposition, the subject is what is spoken about and the predicate is what is affirmed of it. When a subject is considered in a particular respect, the predicate must be assessed in that same context.
“Human beings are bodies” concerns bodily nature; “the human being is a rational animal” addresses the classical account of human essence.
If the predicate simply repeats the subject's meaning in the same respect, the charge of redundancy arises. If it highlights another respect or settles a real dispute, it may provide information.
This distinction is basic to the subsequent analysis.