The following example is merely for the purpose of illustration. You may be able to think of other, completely different examples that are better than the example I have provided here. If you think of a better example, then I encourage you to post your example here.
Historical records indicate that chess player Bobby Fischer "defeated both Mark Taimanov and Bent Larsen with perfect 6-0 scores." Now, let us suppose (purely a hypothetical, and I don't claim to have any evidence whatsoever to support this) that somebody paid Taimanov and Larsen to deliberately lose those games against Fischer. Would that be of interest to historians?
Now, I can imagine that some people might say, "No, that would not be of interest to historians." After all, the actual moves that were made in those games have been recorded. We know what happened. Motives are in the mind of the individual, and not open to inspection. Thus, motives are matters of opinion, not fact.
What I am wondering is ... continuing my example ... why it matters that Spassky lost to Fischer if (again purely as a hypothetical) he was ordered by the leaders of the USSR to lose to Fischer. For example, we can imagine (again purely as a hypothetical) that the leaders of the USSR had a plan to use symbolic events such as chess games to evoke over-confidence among people in the USA.
Now, I can also understand the point of view that identifies motives as being an important part of history. For example, if people stopped watching games played by the highest rated chess players in the world, and chose to instead watch games played by actors who don't know how to play chess and play only the moves that their script tells them to play on the chess board, then we would be witnessing a real shift.
Arguably, if motives are important, then the shift would be good for historians because, while actors are doing their jobs as actors, their real motive (to entertain an audience) is clear. In contrast, Fischer defeating Larsen 6-0 or defeating Spassky is not as significant as it initially would seem, if Larsen and Spassky were trying to lose, and were only pretending that they were trying to avoid losing.
Remember, all of the references to chess are merely for the purpose of illustration. The question is more general. You saw it in the title, and for your convenience I now repeat it below:
Are motives part of history, or is supporting claims about motives too difficult if one wishes to avoid relying upon opinions?
