I was at first baffled by what Whewell could mean by saying the Realists, such as Plato and Aristotle, regarded “Ideal Conceptions as Images of real things.” After all, it was the philosophers Berkeley and Hume who held that general ideas—and ideal conceptions too—were images. Those British empiricists were not realists concerning universals; rather, they denied that there were such things as an abstraction. There is no such process or product as that, which had been put forth by Aristotelians and others.
I think I see now what Whewell is asserting in this last passage you quoted in #5. He is using image more generally than usual. I think he means to assert that on the realist approach one ends up acquiring general ideas, where each is a mirror reflection in the mind of a particular real thing in the world as it is absent mind. That is, there had been, according to the realist, one mental item, a distinct general idea, corresponding to one particular item in the world (which particulars had to be accessed by intellection, not simply sensory perception). It seems Whewell is standing here with Kant against the rationalist tradition holding that we have intellectual intuitions.
Whewell’s charge against realism seems unfair to the Aristotelian tradition of realism, but that would depend on how one understands their claim that universals reside immanently (not transcendently) in particulars. At any rate, Whewell takes himself to have refuted the realists by his Image charge, and perhaps he was aware that in the same stroke he was repudiating the abstraction-skeptics, Berkeley and Hume. In his embrace of the binding of particulars by ideas and conceptions that are much more than names, contrary the nominalist position, Whewell seems to stay pretty close to Kant.* (Scroll down to seventh paragraph from the end of that section.)
I notice that Whewell is not using the terms idea and conception interchangeably. He use them distinctly to mark an epistemological distinction. He writes in Novum Organon Renovatum (the second part of his Philosophy of the Inductive Sciences):
We have given the appellation of Ideas to certain comprehensive forms of thought,— as space, number, cause, composition, resemblance,—which we apply to the phenomena which we contemplate. But the special modifications of these ideas which are exemplified in particular facts, we have termed Conceptions; as a circle, a square number, an accelerating force, . . . a genus. Such Conceptions involve in themselves certain necessary and universal relations derived from the Ideas just enumerated; and these relations are an indispensable portion of the texture of our knowledge. But to determine the contents and limits of this portion of our knowledge, requires an examination of the Ideas and Conceptions from which it proceeds. The Conceptions must be, as it were, carefully unfolded, so as to bring into clear view the elements of truth with which they are marked from their ideal origin. This is one of the processes by which our knowledge is extended and made more exact . . . . (Chapter II, §1)
Now in order to establish any law by reference to facts, we must select the true Idea and the true Conception. For example: when Hipparchus found that the distance of the bright star Spica Virginis from the equinoxial point had increased by two degrees in about two hundred years, and desired to reduce this change to a law, he had first to assign, if possible, the idea on which it depended;—whether it was regulated for instance, by space, or by time; whether it was determined by the positions of other stars at each moment, or went on progressively with the lapse of ages. And when there was found reason to select time as the regulative idea of this change, it was then to be determined how the chance went on with the time;—whether uniformly, or in some other manner: the conception, or the rule of the progression, was to be rightly constructed. Finally, it being ascertained that the change did go on uniformly, the question then occurred what was its amount:—whether exactly a degree in a century, or more, or less, and how much: and thus the determination of the magnitude completed the discovery of the law* of phenomena respecting this star. (Chapter V, §2)
The construction of the Conception very often includes, in a great measure, the Determinations of the Magnitudes. (Chapter VI, §1)
I gather that contemporary scholars are divided as to how far Whewell’s idealism is like that of Kant. Robert Butts writes in his Introduction to William Whewell – Theory of Scientific Method:
Fundamental Ideas are what the activity of mind contributes to knowing. Whewell likens some of them, notably space, time, and number, to Kant’s forms of intuition. Others, for instance the ideas of cause and likeness, play for Whewell something akin to the role of Kant’s categories, though he does not use Kant’s term to designate them. . . .
What is significant for our purposes is not this evident similarity of his doctrine to Kant’s (which Whewell readily admits), but rather the novel features of Whewell’s position, which his subsequent discussion brings forth. . . .
[Whewell’s] view that empirically observed truths can become necessary ones, or as Whewell says elsewhere, that a posteriori truths become a priori appears to be quite incompatible with the Kantianism of his general conception of the Fundamental Ideas. . . .
To understand this initially astonishing view, one must comprehend in detail both the nature of Whewell’s Fundamental Ideas and the character of necessity that they bestow on some propositions of fact. . . .