Lesson 14 (Dec. 15, 22) Scientific Statements in the Past Tenses

Review: Statements in the Present Simple The present simple is used for regular actions and regular processes: – He studies physics six hours a week. The present simple is used for factual and general statements: – Water freezes at 0  Celsius. (fact) It is also used for theorems and definitions: – The induced electromotive force in a closed circuit (theorem) equals the time rate of change of the magnetic flux. The present simple is also used for observations and in descriptions of experiments: – The liquid in the test-tube weighs 55 grams. General rule: Always use the Present Simple unless there are good or compelling reasons for using another tense.

Present versus Past Tenses Use present tenses to describe your present work or established facts. Zhores Alferov, Nobel Lecture, 2000.

Present versus Past Tenses Past tenses are almost always reserved for describing past works, historical facts and results, etc. Zhores Alferov, Nobel Lecture, 2000.

Scientific Statements in the Past Tenses In certain kinds of scientific writing the past tenses are used. These are mainly: – Histories of science and technology; – News articles about science and scientists. In journal papers, it is also common to refer to previously published work in the past tenses. – Use of the past tenses is usually found in the Introduction.

Scientific Statements in the Past Tenses

Forms of the Past Tenses The Past Simple – Active The storm damaged the harbour last week. They tested the new batteries yesterday. They did not complete the work on time. Did they finish the analysis yesterday? – Passive The harbour was damaged by the storm. The new batteries were tested yesterday. The work was not completed on time. Was the analysis finished yesterday?

Forms of the Past Tenses The Present Perfect – Active The water has already boiled for ten minutes. The new microscopes have arrived. The examinations have not begun yet. Has the water boiled? – Passive This has been known for many years. All the acids have been identified. Fermatt's last theorem has never been proved. Has the analysis been completed?

Use of the Past Simple The Past Simple is normally used to describe actions which happened in the past and are now finished.  The first satellite, Sputnik 1, circled the earth 200 times. The action is understood to be finished because Sputnik 1 is no longer going round the earth. More often, the Past Simple is used together with a time- phrase that refers to the completed past: – Explicit time-phrases e.g. last week, yesterday, at 10 am, etc. – Implicit time-phrase  Early generators produced only direct current.  The first generators produced only direct current.

Workshop 1: The Past Simple Rewrite, putting the verbs in brackets into the correct form (either active or passive). Example: – The crucible.... with a clamp. (hold) – The crucible was held with a clamp. 1.The sun at 5.34 this morning. (rise) 2.The eclipse at 8.20 P.M. on 1st July, (see) 3.He the apparatus the day before the experiment. (set up) 4.The lesson by most of the class. (not understand) 5.Early pumps by the wind. (drive) 6.The first planes at less than 100 km per hour. (fly) 7.The measuring-rod in the previous experiment. (break) 8.Originally, the tower of Pisa at such an angle. (not lean) 9.This beam-balance a great deal of money. (cost)

Use of the Present Perfect As a general rule, the Present Perfect is used to describe past events at non-specific time:  Medicine has made great progress in the last twenty years.  Scientists have not yet discovered a cure for AIDS.

Use of the Present Perfect A more important use of the Present Perfect is to describe facts/events that take place one after another. – First read the following and try to determine the sequence of events:  After a distillation flask is filled with water, it is heated over a low flame. Distilling is stopped when 3 cm of the distillate is collected. 0 cm Filling Heating -- Distillation 3 cm Distillate

Use of the Present Perfect  After a distillation flask is filled with water, it is heated over a low flame. Distilling is stopped when 3 cm of the distillate is collected. Using the present perfect gives a better sense of the sequence of events:  After a distillation has been filled with water, it is heated over a low flame. Distillation is stopped when 3 cm of the distillate has been collected. 0 cm Filling Heating -- Distillation 3 cm Distillate

Workshop 2: The Present Perfect Rewrite these sentences, putting the verbs in brackets into the correct Present Perfect form (active or passive). Example: – Medicine (make) great progress in the last twenty years. 1.The whole area (already photograph) from the air. 2.Fortunately, the voltmeter (already mend). 3.The students (just complete) a long experiment. 4.The generator (break down) twice this week. 5.Chemists (develop) many synthetics during the last few years. 6.The examination results (just publish). 7.The World Health Organization (supply) aid to many countries. 8.Since its invention nearly two hundred years ago, the steam engine (become) the most important single source of power that man (ever know). has made

More Use of the Present Perfect To describe activities carried out a little while before now or just before now. – A description of the new alloy has recently been published. – The research team has just published a description of the new alloy. Therefore, the Present Perfect is usually used with just and recently. Compare the two: – A description of the new alloy has recently been published. – A description of the new alloy was published last month. Now Time has recently been published ? was published last month

More Use of the Present Perfect To describe activities carried out at some unstated or unspecified time before now: – Man has gone to the moon. – A network of communication satellites has been established. – The minister has approved the new plan. It is used when it seems more important to state the fact that something has been done, rather than when it was done. Now Time ? has been to the moon network has been established has approved the plan possibly long but unimportant time period

More Use of the Present Perfect To describe activities starting some time in the past, continuing until now, and possibly continuing for some time in the future: – Medicine has made great progress in the last twenty years. Compare: – Taiwan’s semiconductor industry has existed since – Taiwan’s semiconductor industry has existed for forty years. – Taiwan’s semiconductor industry first existed in Time 1970 first existed has existed

Workshop 3: The Present Perfect Change these sentences into the Present Perfect, using the word or words in brackets. Here is an example: – This was known forty years ago. (for) – This has been known for forty years. 1.This was known in (since) 2.The experiment was completed a little while ago. (just) 3.The generator broke down on Monday and Tuesday. (twice this week) 4.The examination finished five minutes ago. (just) 5.The railway line was closed in (since) 6.The apparatus was repaired in January and May. (two times since) 7.The tunnel was closed 80 years ago. (for) 8.The experiment was not successful each time. (still not)