If the shared aspect is not part of the essential nature, it is an additional quality. The source develops two important groups: sensory qualities perceptible through the external senses, and intellectual qualities understood through the mind.
Sensory quality: Similar redness of flowers, quietness of voices, or softness of fabrics.
Intellectual quality: Similar intelligence, forbearance, or courage of people.
Remember that the nature of the two terms and the nature of their shared aspect are separate questions. Two visible human beings may be compared in courage, an intellectual aspect in this discussion.