As an Oxford theologian, Ockham was preoccupied with the works of Scotus. Few of Ockham's important philosophical or theological doctrines can be fully understood without reference to Scotus's views. [In this respect the relationship between Ockham and Scotus is reminiscent of that between Scotus and Henry of Ghent. Scotus serves as the default starting point for Ockham as Henry does for Scotus. This of course doesn't imply in the least that Ockham is just a heterodox Scotist, any more than Scotus is just some kind of Henrician. What it implies is that, for most of the great medieval thinkers, reading widely is essential for grasping the author at hand. One can read much of Descartes or Hume or Husserl in relative isolation and grasp at least a great deal of their thought. But if one picks a given medieval philosopher to read in isolation one is overwhelmingly likely to misunderstand or fail to grasp a great deal of what is being said. Most works of medieval philosophy and theology are not self-standing treatises but entries in a vast discussion and debate. Even though the debater usually tries fairly to sum up his opponents' points, we really need to listen to the other participants to properly follow it. This is true even for Aquinas and his readers often unfortunately fail to notice it. However it's less true for Aquinas than for most other thinkers of the time. Aquinas doesn't use, say, Albert as his default starting point in the way mentioned here, and the monumental character of his his greatest works can produce the illusion of independence from his context.] But Ockham's citation practice serves to conceal the extent of the influence. Ockham often borrows the basic elements of Scotus' view tacitly, naming Scotus only in connection with disagreements, even when the point in dispute is minor. Most notably, Ockham disagrees with Scotus on the problem of universals: Ockham denies the existence of common natures and attacks realism. But even when he disagrees with Scotus, his respect is evident; for example, when treating universals, he takes care to distinguish misinterpretations of Scotus from the views themselves, which he quotes extensively. Once, when criticizing Scotus, Ockham remarks that Scotus probably would not have disagreed, given his great knowledge of logic. [This almost seems to obscure the importance of the rift on universals, which permeates the two philosophies and their differences in tone and emphasis as well as substantive content to a degree impossible to overstate.]
But respectful as he was, Ockham shows no special reverence in citing Scotus; he normally refers simply to John or Brother John, in De connexione virtutum and in his early Reportatio commentary on the Sentences. Subsequently Ockham does refer to Scotus as the Subtle Doctor, adding that he is so called because he exceeds others in the subtlety of judgment, but noting that Scotus is not an authority for him in the same way as he is to his followers. Ockham does not mince words when he thinks Scotus is mistaken.
Ockham's manner of reference contrasts with that of Adam Wodeham, his student, in about 1330, who refers to Scotus as "Our Doctor," - that is, the Franciscan Order's doctor. Ockham did theology precisely in the period when Franciscans first began to venerate Scotus. Ockham's less deferential approach to Scotus may explain in part the hostility with which he was regarded by such fellow Franciscans as John Reading and Walter Chatton. The dispute between Ockham and Scotus's defenders was as much a matter of attitude as of doctrine, and it has served to obscure both the extent of Ockham's debt to Scotus and the degree to which Ockham influenced Scotists, such as Reading and Chatton. [It's hard for me not to read into this some connection with Ockham's attitude, his lack of reverence and quickness to label disagreement heresy, towards the Pope. I rather suspect that when people try to trace the Reformation back to Ockham the similarity they find between himself and the Reformers is more one of personality and attitude than in the real content of his thought. Aquinas and Scotus were both saints; Ockham was not.]
If Ockham's criticisms of Scotus were a product of intimate familiarity, his knowledge of Aquinas was much more limited. Indeed, instead of discussing Aquinas, when contending against views associated today with Aquinas, he often has other medieval authors in mind . . . [Wood mentions Giles of Rome, Richard of Middleton, and Peter of Spain here. It should go without saying that this same point applies when reading many authors of the time.]
Studies showing that a superficial reading of Ockham understates his debt to Scotus should not be taken as evidence of a lack of originality. They are a sign rather that we cannot understand Ockham without knowing Scotus. In the end, a "strong reaction" may be as important a manner of developing a philosophy as there is.
It's a good idea to read Ockham even if you think his philosophy is fundamentally flawed, as I do. First, because one can't read much of him without realizing very clearly that he was a great genius, greater than many more-studied moderns. He may be wrong, but he's smart. If Scotus' defining quality is his subtlety, and it surely is, the overwhelming impression given by reading Ockham is that he is sharp, extremely, penetratingly, keenly sharp. He cuts through all the intellectual morass and puts his scalpel right into the heart of the problem in play.
Second, because although he is most famous for his razor Ockham makes an excellent whetstone. My doktorvater T.B. Noone (from whom I also took courses in Bonaventure, Scotus, and Ockham), has said in my hearing many times that you can't know if you're really a Scotist without studying Ockham extensively. In a sense you have no right to cleave to a position before having confronted its most trenchant critique; in a similar way any metaphysician ought to seriously confront Nietzsche. In my opinion Scotus makes the most powerful case for realism and Ockham gives the best counterpoint. As a kind of mirror-image inversion of Scotism Ockham is extremely useful for the Scotist, but the Thomist would do well to consider him too. Most Thomists typically read few other scholastics and see Thomas as superior to all competitors, but for them those competitors are usually the ancients and the moderns. Of course I think that Thomists should read Scotus, but for expansion and correction, rather than sheer contrast. Ockham provides a real alternative philosophy that inhabits the same intellectual world as Thomas, with the same habits of argument and the same authorities, but with grossly different arguments and conclusions. Coming to grips with those arguments, rather than merely rejecting the conclusions, will make a better Thomist (even if dealing with Ockham will make you more likely to depart from the letter of the Summa, which is not suited to handle all objections).
Third, Ockham may be helpful simply in understanding Scotus, in a different way than the helpfulness of modern scholarship. Scotus is subtle; he's also disorganized and a poor writer; reading him is harder even than the intrinsic difficulty of his thought requires. Ockham, by contrast, is limpid and straightforward, and seeing how he approaches a Scotistic problem can clarify for us exactly what Scotus himself is up to (reading later Scotists can have the same salutary effect), even when his critiques and his own solutions turn out to be too neat and oversimplified to match reality. Along these lines, reading Ockham is just more enjoyable than reading Scotus (and many other scholastics), at least in certain moods when one is not inclined to relish the feeling of being lost in the woods.