mental object vs knowledge

mental object and knowledge both are nouns.

Word	Noun	Adjective	Verb	Adverb
mental object	Yes	No	No	No
knowledge	Yes	No	No	No

As nouns, knowledge is a hypernym of mental object; that is, knowledge is a word with a broader meaning than mental object:

mental object: the sum or range of what has been perceived, discovered, or learned
knowledge: the psychological result of perception and learning and reasoning

Other hypernyms of mental object include cognition, noesis.

mental object (noun)	knowledge (noun)
the sum or range of what has been perceived, discovered, or learned	the psychological result of perception and learning and reasoning