In humans, the ethos associated with cultural, ethical, and spiritual life comes interwoven with what I have called “animal imagination”, tied to our organic being. The kind of imagination at issue here is not the modern, post-Romantic notion associated with artistic creativity, but part of the basic functioning of many animals. Aristotle associates it with what he calls the “common” sense, which again is not what we call common sense, but rather something fundamental to all perception, that also comes into play in the formation (what Kant would call synthesis) of perceptual wholes from the input of multiple senses. Aristotelian “imagination” involves activations of the common sense in the absence of inputs from external sense. It plays an essential role in memory and dreams. Like much in Aristotle, this is not really an explanatory theory, just an interpretive description of things we experience in ordinary life.
Aristotle is concerned to distinguish imagination from opinion, precisely because there is a close connection between the two. Much later, Spinoza essentially identified opinion with imagination. Aristotle emphasizes that opinion involves an additional element of belief that is not inherent to all imagination. He says there are animals that have imagination but no belief.
Opinion is closely related to Aristotelian practical judgment, although the latter classically refers to a deliberative process whose outcome is action rather than belief, whereas opinion is a kind of belief that is not knowledge. Opinion may be a result of past deliberation or reflection, but very often it is more or less spontaneous. I think Spinoza means to suggest that our less reflective opinions arise from a kind of imagination. Like practical judgment, imagination is concerned with particulars.
Spinoza especially brings out the connection of imagination with emotion. It seems to me these are strongly interdependent. Our emotions both shape our imaginings and are shaped by them. These are what mainly guide our initial responses to things, and we have this in common with other animals.
Even after we have more developed, reflective views of things, there is still an element of spontaneous imagination in any application of those views to new particulars.
Emotion is strongly connected with our apprehensions of value. Again, there are dependencies in both directions. Emotion is a source of many valuations, especially initial ones; but valuations also help shape emotion.