45. Principle/principal

As these two sound completely alike, spelling mistakes are not uncommon. Principle is a noun and means the motive guiding an action or attitude. He looks narrow-minded, but we have to respect his principles. It can also be the basic element: I am not worried about the extra 50 cents, it's the principle that bothers me. Principal as adjective means main, chief, first, foremost: Their principal export is bananas. As a noun it means the head of an institution, usually of a school or college: Let's see the Principal about Willie's bad exam results. In business an agent may refer to the firm or person he represents as his principals: We are authorized to sign on behalf of our principals.

46. Question/query

A question is a straight request for information. The person asking it may know something about the subject; he may know nothing. A query is the result of some doubt in the mind of the speaker or writer who usually knows something about the subject. Clever you and I, listening to the lecture on The Advantages and Risks inherent in Pressurized Water System Nuclear Reactors', may afterwards raise a query. Jack over there, who slept solidly throughout the talk, will wake up and ask a question.

47. Readable/legible

Readable is easy to read because of style: The highly complicated subject was treated in a readable manner. If you want to make sure that your books are read by a wide audience, you must make them readable, i.e. easy to understand, a pleasure to read. Legible is also easy to read, but because the printing or writing is clear: Some pages in this old bible are hardly legible.

48. Small/little

Small is the neutral, general-purpose word, but little has an emotional element and conveys a personal attitude to the object. They have a small fox terrier describes size in a detached, matter-of-fact way. You should see their little cocker spaniel indicates that the speaker is rather fond of the little fellow. Another use of little, often unconnected with physical size, is as reinforcement of a negative opinion. When you say 'He is a nasty man!' you are obviously not over-impressed by his charm. When you hiss 'He is a nasty little man!', he must be very nasty indeed.

49. Large/big

The difference is the same as that between small and little. Large is for sober comment; big for a more personal or emotional opinion. An advertisement for a house, for example, may mention large dining room . When you have seen it, you are likely to tell your friends: 'it's got a big dining room'.

50. Stimulus/stimulant

As you can guess, these two words have something to do with getting things to move a bit faster, raising the interest level and other developments in the right direction. Stimulus is the abstract term: His enthusiasm was a tremendous stimulus to all of them. Stimulant is the concrete article, usually something you swallow to prevent you from going to sleep.

51. Tall/high

Both mean a certain distance from the ground. Tall implies a narrow base, something slender: a tall chimney, a tall mast, a tall person. High has a base of a certain width: a high wall, a high mountain, a high fence. When you are in doubt about someone who is tall but by no means slender (Fatty weighs 150 kilos), call him big. If a person is described as 'high' it means that he or she has had too much alcohol or drugs.