- enough, sufficient, sufficiently1. Enough functions as both an adjective and an adverb, whereas sufficient requires modification as sufficiently. As an adjective (or modifier), enough will normally serve, but sufficient is more idiomatic when a more qualitative point is being made. For example, in the sentence
• There will inevitably be concerns that the courts' powers are not sufficient for worthwhile penalties to be imposed —Bristol Evening Post, 2007sufficient implies a stronger element of disapproval of the inadequacy than would be the case if enough had been used. Enough also has two grammatical characteristics that are not shared by sufficient: (1) enough cannot be used with mass nouns denoting quantity, such as number, supply, etc., preceded by the indefinite article; you can say a sufficient number but not ☒ an enough number, and (2) enough can be placed postpositively (after the word it qualifies), as in They have money enough for a holiday and They do not have a large enough house, which places a greater emphasis on the commodity or attribute in question.2. Choice between enough and sufficiently when they are used as adverbs is normally determined by the degree of formality needed, sufficiently being the more formal. The main grammatical difference between them is that enough is placed after the word it qualifies when this is an adjective or another adverb: He was not firm enough and She did not sing well enough but He was not sufficiently firm and She did not sing sufficiently well. There is no difference in use when they qualify verbs or clauses: They are not working enough and They are not working sufficiently.
Modern English usage. 2014.