Select the single English word that best substitutes the phrase "express a proposition, theory, or idea in clear or definite terms" in formal communication.

Introduction / Context:
In formal English, especially in academic and legal contexts, it is important to choose precise verbs for describing how ideas are expressed. This question asks for a one word substitute for the phrase "express a proposition, theory, etc. in clear or definite terms". Such substitutes are valuable in essays, reports, and examinations. The learner must distinguish between related verbs like publish, postulate, proclaim, and enunciate, all of which involve communication but with different nuances.

Given Data / Assumptions:
- The phrase to be replaced is "express a proposition, theory, etc. in clear or definite terms". - Four single word options are given. - Only one option fits the requirement of expressing something clearly and precisely. - The context is formal explanation or statement of ideas.

Concept / Approach:
The core idea in the phrase is clarity and definiteness of expression. The correct word must carry the sense of stating ideas distinctly, not merely suggesting them or making them public. "Enunciate" is a verb that means to state or set forth an idea clearly and distinctly, both in terms of articulation and in conceptual clarity. The other options each carry a different emphasis: "publish" is about making something public, "postulate" is about assuming something as a basis, and "proclaim" is about announcing loudly or officially. Recognising these subtle differences is the key to selecting the correct term.

Step-by-Step Solution:
Step 1: Analyse the phrase. It highlights expressing a proposition or theory in clear or definite terms. Step 2: Option a, "publish", means to make information or writing available to the public, such as printing a book or releasing a report. It does not necessarily imply clarity in the expression itself. Step 3: Option b, "postulate", means to suggest or assume something as a basis for reasoning or argument. It focuses on proposing a starting point, not on making the language clear. Step 4: Option c, "proclaim", means to announce something publicly or officially, often in a loud or emphatic way. Again, the emphasis is on public declaration, not precise formulation. Step 5: Option d, "enunciate", means to state or express an idea in a clear, definite, and often formal manner; it also refers to pronouncing words clearly. Step 6: Therefore, the only verb that directly matches the notion of expressing an idea clearly and definitely is "enunciate".

Verification / Alternative check:
To verify the choice, imagine writing a sentence for a formal report: "The policy should clearly enunciate the rights and responsibilities of all stakeholders." Here, "enunciate" fits perfectly because it suggests clearly stating these matters. Replacing it with "publish" or "proclaim" would not match the nuance of carefully formulated clarity, and "postulate" would imply an assumption rather than a clear statement. This comparison confirms that "enunciate" is the correct one word substitute for the given phrase.

Why Other Options Are Wrong:
Option a "publish" is wrong because it stresses making material public, not the clarity of its expression. Option b "postulate" is wrong because it refers to assuming or suggesting a principle to build an argument on, rather than clearly stating it in definite terms. Option c "proclaim" is wrong because it indicates a public or official announcement, often with emphasis, but does not focus on careful, precise wording.

Common Pitfalls:
Candidates sometimes choose words like "publish" or "proclaim" simply because they are common in news and media language. However, one word substitution questions often require attention to subtle nuances. The safest strategy is to match the key ideas in the phrase, here clarity and definiteness, to the core meaning of each option. It is also useful to recall example sentences where these verbs naturally occur, as those real contexts usually reveal the differences more clearly than a bare dictionary definition.

Final Answer:
The correct one word substitute is enunciate.