Myles Tierney has told me about a perspective on exact categories, in the 1960s, that I had not understood. I probably still do not see it very much the way it looked then. So I ask about it here. What were the reasons for studying exact categories in the 1960s? Here is what I used to think: Every additive category with a generator has a faithful functor to the category of Abelian groups. MacLane had explored this idea in 1950. Then Grothendieck's Tohoku paper axiomatized Abelian categories in a more useful way for homological algebra, and showed that all sheaf categories satisfied the axioms (i.e. sheaves of Abelian groups on topological spaces, and the key theorem says they have enough injectives). That created two reasons to look for a non-additive generalization. First, to extend from Abelian groups to all groups, for use in non-Abelian cohomology. (MacLane had already hinted at replacing Abelian groups by all groups in 1950). And second to axiomatize sheaves of sets. The exact category axioms were a promising non-additive analogue to the Abelian category axioms. And I have always thought of the Abelian category embedding theorems as proving that, if you want to, you can think of Abelian categories as concrete categories with the natural limits and colimits. Myles did not disagree with any of that but he put it this way: Not all categories enriched in Abelian groups are so nicely embeddable in the category of Abelian groups, but the Abelian categories are. This suggested a general question, when does an enriched category embed nicely in the enriching category? And Myles had a good description of which Abelian-group enriched categories are Abelian: the exact ones. So the exact category axioms became an approach to this problem. To me this question seems very different from looking for a non-additive analogue of Abelian categories. Am I wrong about that? How did this question look in, say, 1970? How did it look at Dalhousie? Thanks, Colin