The phrase "observe a principle" is correct and usable in written English.
You can use it whenever you want to express the idea of someone or something adhering to a rule, belief, or standard. For example, "As a teacher, he always strove to observe the principle of fairness in the classroom."
Asked if first children should, in general, remain "off-limits", Earnest agreed: "I think a lot of people observe that a principle like that is I think pretty much common sense".
We also observed a significant governing principle of protein folding in terms of the minimization of the sum of the all pairs shortest path (APSP) for all the residues of the protein.
This phenomenon you could call, in honor of the particle physicist, the Heisenberg Unpleasantness Principle: Observing a market pattern makes it stop.
Our approach is neither "vague" nor "indistinct" but based on a set of precise principles laid out in our declaration, such as the need for all parties to observe international law, a principle whose political implications for human rights in the region are vast.
As late as the 2nd century bce, Han scholars were still attacking the Qin family structure as failing to observe the principle of filial piety, a cardinal virtue in the Confucian moral code.
Using pom1 as a proof-of-principle, we observed a maximal increase of Purg1-pom1 transcripts after uracil addition within less than 30 minutes, and a similarly rapid decrease after uracil removal.
The impulse to observe the principle of innocent until proven guilty can be an admirable one.
The paradigmatic description of contextual parameters in an earlier section has demonstrated that precision and orderliness are built into the paradigmatic method of representation: there has not arisen any need to add or subtract from those conventions; all that is needed is to observe its principles as a language dedicated to presenting a specific kind of information.
A proof of principle is given by observing a prototype that was milled into a copper bar.
We observed an 'exchange of dissipation' principle in the sense that an increased numerical dissipation implied a reduction in the optimal Smagorinsky parameter.
