a / an In modern written English, we use a before a word beginning with a consonant sound, however it may be spelled (a frog, a university, a euphemism). We use an before a word beginning with a vowel sound (an orange, an hour). At one time, an was an acceptable alternative before words beginning with a consonant sound but spelled with a vowel (an one, an united appeal), but this usage is now entirely obsolete An was also once a common variant before words beginning with h in which the first syllable was unstressed; thus 18th-century authors wrote either a. | a an In modern written English we use a before a word beginning with a consonant sound however it may be spelled a frog a university a euphemism . We use an before a word beginning with a vowel sound an orange an hour . At one time an was an acceptable alternative before words beginning with a consonant sound but spelled with a vowel an one an united appeal but this usage is now entirely obsolete An was also once a common variant before words beginning with h in which the first syllable was unstressed thus 18th-century authors wrote either a historical or an historical but a history not an history. This usage made sense in that people often did not pronounce the initial h in words such as historical and heroic but by the late 19th century educated speakers were usually giving their initial h s a huff and the practice of writing an began to die out. Nowadays it survives primarily before the word historical. You may also come across it in the phrases an hysterectomy or an hereditary trait. These usages are acceptable in formal writing. able The construction able to takes an infinitive to show the subject s ability to accomplish an action We were able to finish the project thanks to a grant from a large corporation. The new submarine is able to dive twice as fast as the older model. Some people think able to should be avoided with passive constructions involving forms of the verb be The problem was able to be solved by using a new method. Since the problem has no ability to accomplish an action this reasoning goes it is not able to do anything therefore able to should not be used. In such cases you can usually substitute can or could The problem could be solved by using a new method. Keep in mind however that passive constructions using the verb get ascribe a more active role to their subjects and here you can use able to He was able to get himself accepted by a top law school about The preposition about is traditionally used to refer to the relation between a .
