Care must be taken not to confuse de with da.
Examples.--_La libro de Petro_ = The book of Peter, _or_, Peter's book. _La domo de mia kara patro_ = My dear father's house.
Origin or Dependence = _Of_, _on_, _from_.
Examples.--_Ĝi dependas de la nombro de vortoj_ = It depends on the number of words. _Tio venis de_ (or, _el_) _lia unua eraro_ = That came from his first error. _Li estas doktoro de medicino_ = He is a doctor of medicine. _Li venis de_ (or, _el_) _Parizo kaj nun iras al Berlino_ = He came from Paris and is now going to Berlin. _Kaj Dio diris: "Kolektiĝu la akvo de sub la ĉielo en unu lokon"_ = And God said: "Let the waters (water) (from) under the heaven be gathered together (collect itself) into one place."
Examples.--_For de tie ĉi, fripono!_ = Away from here, rascal! _Li forestas de tie ĉi_ = He is away from here. _Li staris meze de la malamikoj_ = He stood in the midst of the enemy. _Proksime de la domo staris arbo_ = Near (to) the house stood a tree. _Ne malproksime de la dometo staris preĝejo_ = Not far from the cottage was (stood) a church.
Examples.--_De tiu tempo_ = From (since) that time. _De la kreo de la mondo_ = Since the creation of the world. _De tri semajnoj mi estas malsana_ = For three weeks I have been (am) ill.
Examples.--_Li eksaltis de surprizo_ = He started (jumped) with surprise. _Li mortis de febro_ = He died of (from) fever. _Kaŭze de tio_ = Because of (due to) (owing to) that.
Agency = _By_ (after a passive verb, to show the _agent_). To show the _means_ per is used.
Examples.--_Mi estas amata de mia patro_ = I am loved by my father. _La domo konstruita de mia patro estas kovrita per ardezoj_ = The house built by my father is covered with slates.
Example.--_Apartigu la pajlon de la fojno_ = Separate the straw from the hay.
As a prefix, _de_ signifies "off," "from," as:--_Li deprenis la libron de la breto_ (or, _li prenis la libron for de sur la breto_) = He took the book off the shelf. _Li demetis la ĉapelon_ = He took off his (the) hat.
Dum, whether used as a preposition or conjunction, always relates to duration of time (see note below).
Examples.--_Dum la tuta tago_ (or, _La tutan tagon_) _li restis sola_ = During the whole day he remained alone, _or_, He remained alone the whole day. _Dum_ (or, _En la daŭro de_) _kelkaj monatoj, ŝi ne eliradis el sia ĉambro_ = During (for the space of, for) some months she did not leave (go out of) her room. _Li dormis dum la tuta koncerto_, or, _Li dormis la tutan koncerton_ = He was sleeping during the whole (all through the) concert. _Dum ilia konsiliĝo_ (or, _Dum ili konsiliĝis_) _mi restis en la apuda ĉambro_ = During their consultation (_or_, whilst they were consulting) I remained in the adjoining room.