- at dawn; at six; at midnight; at 4:30. at sixteen / at the age of sixteen; She got married at seventeen. on Monday; on 4 June; on Christmas day. at night; at Christmas; at Easter. We arrived on the morning of the sixth. this / next Monday, etc.; any Monday; one Monday»
[«at,» «on»: «at a time» («en un tiempo»); «at an age» («a una edad»). «on a day / date» («en un día / fecha). Excepciones: «at night,» «at Christmas,» «at Easter.» «on the morning / afternoon / evening / night of a certain date.» Y también es posible decir: «this / next Monday, etc.», «any Monday,» «one Monday.»]
2. by a time / date / period. The train starts at 6:10, so you had better be at the station by 6:00. By the end of July I’ll have read those books. Before signing this … (preposición); Before you sign this … (conjunción); I’ve seen him somewhere before … (adverbio).
[«by,» «before«: «by a time«/»date«/»period» = «en ese momento o antes/no más tarde de esa fecha.» A menudo implica «antes de ese momento/fecha»: «The train starts at 6.10, so you had better be at the station by 6.00.» «by» + una expresión de tiempo se usa a menudo con un tiempo de perfecto, particularmente el futuro perfecto: «By the end of July I’ll have read all those books.» «before» puede ser preposición, conjunción o adverbio.]
3. The 8.15 train started on time, (It started at 8.15). Passengers should be in time for their train; I arrived at the concert hall in good time, (Perhaps the concert began at 7:30 and I arrived at 7:15
[«on time,» «in time,» «in good time«: «on time» = en el tiempo fijado, ni antes, ni después; «in time«/'»in time for» + «nombre«‘ = no tarde («not late»); «in good time (for«) = «with a comfortable margin«]
4. «on arrival,» «on arriving,» «on reaching,» «on getting to.» «on arrival» / «on arriving,» he … = «when he arrives / arrived, he …» On checking, she found that some of the party didn’t know the way; On hearing / Hearing that the plane had been diverted, they left the airport.
«on arrival,» «on arriving,» «on reaching,» «on getting to«: «on arrival«/»on arriving, he …» = «when he arrives / arrived, he …» on puede también usarse similarmente con el gerundio de algunos otros verbos (principalmente verbos de información); El on en la última frase podría omitirse.
5. At the beginning of a book there is often a table of contents; at the end there may be an index. In the beginning / at first we used hand tools. Later we had machines. At first he opposed the marriage, but in the end he gave his consent.
[«at the beginning/end,» «in the beginning/end,» «at first«/»at last«: «at the beginning/end (of)«/»at the end (of)» = literally «at the beginning»/»end»; «in the beginning/at first = «in the early stages,» (implica que más tarde se produjo un cambio); «in the end/at last» = «eventually»/»after some time».]
A Practical English Grammar (A.J. Thomson & A.V. Martinet) 