This section opens with Sellars pointing out that, on the view set out in the fourth section, we can begin to understand the general temptation that exists to assimilate sense impressions to minimal conceptual representations due to the fact that the sense impression of something does not possess the typical qualities of that thing any more than a conceptual representation does. Having opened with this point Sellars rapidly proceeds to a distinct second one. This concerns the fact that "sense impressions" have only an analogical relationship to perceptible attributes of physical objects.
This point about the analogical relationship of the impression to the perceptible attribute is discussed in terms of the point that to speak of the impression "of" a red rectangle when the impression itself is neither red nor rectangular involves using the terms "red" and "rectangle" in an odd way. Sellars terms this use "adjectival". The point that he wishes to get at with this apparently purely verbal reference is that the general acceptance of the notion of "sense impressions" is as part of a causal story and in this causal story the sensory impression is taken to be a non-conceptual state which has a red and rectangular physical object as its standard cause. Sellars objects to this rendering of the sense of the "sense impression" as this requires it to be understood as a definite description through causal connections rather than as an analogical use of predicates and leads in the direction, once again, of "crude" (as Sellars now terms it) physicalism.
The third point that Sellars makes builds on this second one. Now Sellars points out that the causal story is also one that incorporates a kind of typical reference (what kind of cause could be expected) but that this is also odd in the case under consideration. After all, if the suggestion is that the sense impression of the red rectangle is, typically, produced by a physical surface that is red and rectangular then we reduce the description of the impression to a discussion of what it is that has produced it and, further, do so in a way that assumes that a certain feature of the physical surface can be basically identified with the sense impression (an odd assumption in many respects).
Sellars' fourth point is that when we say we have a conception "of" a red rectangle we are not making the same kind of reference to "physical object predicates" as we are when we speak about the sense impression "of" a red rectangle. This is followed by the fifth point that the temptation we are under when we conflate sense impressions with minimal conceptual episodes (something Sellars has consistently argued against in this chapter) is one relating to the impressions as if they were conceptual items of our "inner speech".
The final point of the fifth section concerns the fact that what is in common between "impression of" and "conception of" is that both are logically intensional as neither can lead to a direct inference that there are any objects of the sort "referred to" around. This intensional equivalence does not lead to an intentional connection as only the conception has intentionality. (This last point leads already to considerations that Sellars will take further in the second chapter of Science and Metaphysics.)