恐怕：副词，不能受“很”修饰，通常放在主语后、谓语前或句首，后接小句或动词短语，常与“会、要、得、是、不、未必、来不及”等组合，表示说话人较有把握的推测，或委婉地表示担心、歉意、不同意见；它不表示身体或心理上直接的恐惧。怕：动词兼副词。作动词时可带名词、动词短语或小句宾语，常与“冷、黑、麻烦、生、死、人、输、迟到”等组合，口语性强；作副词时表示推测或“唯恐”，多用于口语。害怕：动词/形容词性词语，表示心理上的恐惧，常作谓语、宾语（如“感到害怕”）或补语，可受“很、非常、有点、极了”等程度词修饰，也可带“失败、孤独、黑暗”等宾语；它只表示恐惧情绪，不表示推测。差异：恐怕偏副词性推测和委婉语气；怕范围最广，兼具体恐惧和口语推测；害怕最强调情绪上的恐惧，程度可量化，不能用于“推测”义。
恐怕 is an adverb; it cannot be modified by 很 and usually appears after the subject, before the predicate, or at the beginning of a clause. It often combines with 会, 要, 得, 是, 不, 未必, 来不及, etc., to express a fairly confident conjecture or a polite worry, apology, or disagreement. It does not express direct physical or emotional fear. 怕 is a verb and also a colloquial adverb. As a verb it can take a noun, verb phrase, or clause as its object and commonly combines with 冷, 黑, 麻烦, 生, 死, 人, 输, 迟到, etc.; it is highly colloquial. As an adverb it expresses conjecture or 'lest'. 害怕 is a verb/adjective-like word expressing psychological fear. It often functions as a predicate, an object (as in 感到害怕), or a complement, can be modified by degree adverbs such as 很, 非常, 有点, 极了, and can take objects such as 失败, 孤独, 黑暗. It expresses fear only, not conjecture. Difference: 恐怕 is primarily adverbial conjecture and polite tone; 怕 has the broadest range and covers both concrete fear and colloquial conjecture; 害怕 emphasizes emotional fear, can be graded, and cannot mean 'perhaps'.