A list of modal verb usage in President Trump's recent speech on the Syrian air strikes. "American" subjects are highlighted.
Modal (auxiliary) verbs (can, could, should, would, must, will, etc.) are an interesting subset of American language, as they are used to indicate "intention" (the way things "ought to" be or "should" be, or an evaluation of what "can" happen). Different modals have different degrees of "modal force."
Here, you'll see that the modal "can" is the most commonly used, often referring to non-American subjects (e.g., "nations of the world" or "our friends"). In the three instances "can" is used in relation to Americans, two are negations ("No amount of American blood..." and "we cannot..."). In the last instance, "can" is used to express a hope, rather than an intention.
By contrast, the other "can" modals are used effectively as threats and evaluations: "The nations of the world can be judged by the friends they keep" or "Increased engagement [...] can ensure that Iran does not profit..."
This distinction is important because it uses our allies and vague "international norms" to express how the world "can" be. Even though the U.S. is certainly an instigator, the modal verb usage implies that we are trying to distance ourselves from taking ownership of these air strikes. We frame this use of force as unavoidable, because of actions taken by other states. The singular use of "would" and "must" in relation to Russia reinforces this further, especially given that they are used so closely together (Russia was supposed to do something, and then they didn't, so they now must do something else).
To make a long story short, we express the necessity of use of force here by saying what we (the US) "cannot" do, and implying what "can" (implicitly "should") happen as a result.
This speech obviously deviates from President Trump's typical language use, but it goes to show the significance of "use of force": even rebels fall in line when they have to justify violence.
(Hoping to do some analysis of news around this air strike tonight as well!)