Knowledge on the part of others is not essential. Any awareness of the abilities, capacities, faculties and powers of others that I might have is not essential to their possession or exercise of them, though it may be essential to their cooperating with me or I with them. Since anything done by anyone is done either knowingly or unknowingly, then the capacity to know is essential to any and all abilities, capacities, faculties and powers of the person, whether these be possessed or exercised knowingly or unknowingly. This might be taken to suggest that some abilities can be regarded as the conscious exercise of more basic abilities, capacities, faculties or powers. Memory is the ability to consciously recollect past knowledge or experience.
Perception is the faculty of conscious exercise of the senses.
These differ in an important respect, perception involves the employment of evident bodily resources, such as the eyes or the ears, whereas memory either employs no bodily resources or employs non-evident bodily resources. To say that abilities, capacities, faculties or powers do not employ evident bodily resources is not to say that they do not employ bodily resources, they may employ non-evident bodily resources. Any abilities, capacities, faculties or powers of the person may employ bodily resources which are evident to some degree. These are, to some degree, evident to me, though I rarely, if ever, attend to them when I speak. It is a fact that the sounds I make when I speak are produced by vibrations of the vocal chords, though my vocal chords are never evident to me.