These words mean to have knowledge of the existence or fact of something. Aware is the broadest term, and may mean having knowledge of something in side oneself or of some external fact or condition. Such knowledge may be based on the evidence of one’s senses or on the intellect: to be aware of hunger pangs; aware of a sharp drop in temperature; aware of a new trend in public opinion.

Conscious at its most restricted is close to aware in indicating the mind’s registering of a sensation, perception or state of affairs: conscious of how dim the room had grown as the twilight deepened; conscious of what the other students thought of her. Even on this level, however, the word may suggest the minimal registering of perception, whereas aware more often implies a keener response or greater alertness that may encompass evaluation or rational judgement: People had been conscious of the problem before, but the new book made them aware of its magnitude. Conscious , furthermore, can apply as aware cannot to the waking state in general, as opposed to a sleeping or comatose state: a local anaesthetic under which a person remains conscious throughout the operation. In a psychological context, the word can apply to those contents of the psyche that are present or available to the ego: a conscious hatred of his mother; slowly becoming conscious of his long-buried feeling of inferiority. Less technically, the word can refer to a deliberate or voluntary judgement: urged to make a conscious choice before events decided the question for them.

Cognizant implies knowledge of a more public character than the other words here considered. To say that one was cognizant of a breeze would be absurdly pretentious, but one may without fear of ridicule claim to be cognizant of new methods in the teaching of foreign languages.

• A union leader ought to be cognizant of the attitudes and opinions of the rank and file.

Cognizant thus suggests a deliberate effort to know, and the things known are usually of some public importance. Mindful , like cognizant a rather formal word, emphasizes the giving of attention more than the acquisition of knowledge.

• Because I am always mindful of my own mistakes, I am tolerant of the mistakes of others; Mindful of the strong opinions of his electorate, the member voted against the measure.

On to is a colloquial expression meaning aware of, especially of something involving deception or skulduggery. It usually expresses a good deal of indignation, if not outright hostility.

• I’m on to you and your fancy ideas about how I should spend my money; you’re nothing but a crook!