present perfect vs simple past

PRESENT PERFECT	SIMPLE PAST
Unfinished state or action She has written the novel since 2008	Finished state/action She wrote the novel from 2008 to 2009.
Unfinished time I haven’t seen Mira this morning yet. (It’s still morning)	Finished time I didn’t see Mira at all this morning. (it’s now afternoon/evening)
Present relevance Mr. Toni has arrived. He’s in the office now.	No present relevance Mr. Toni arrived a few hours ago.
Indefinite time I’ve been to Lombok twice.	Definite time I went to Lombok in 2007 and 2010.

¨  The past simple tense may describe completed activities and past situations

¤  In 1976, 60% of families were couples with children.

¤  In 1981, 34% of children aged 20-24lived with their parents.

¨  The past simple may describe activities without linking them to the present

¤  They completed the research in 1972.

¤  They arrived yesterday.

¨  With past simple verbs, the time may be specified

¤  They completed the research in 1972.

¤  They arrived yesterday.

¤  The number of one person households grew last year.

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The present perfect tense may describe activities or situations which began in the past and are still continuing

¤  The number of one person households has grown.

¤  Over the past twenty years, the average size of households has fallen.

¨  The present perfect may describe completed activities whose impact is felt in the present

¤  They have completed the research. (meaning: a short time ago; here it is).

¤  They have arrived. (meaning: a short time ago; here they are).

¨  With present perfect verbs, indefinite time expressions may be used

¤  They have just completed the research.

¤  They have already arrived.

¤  The number of one person households has grown recently.