The passive was in some of the older schemes expressed by means of various prefixes, infixes or suffixes, but is in most schemes nowadays expressed in the same way as it is generally in Romanic languages and English, by means of the auxiliary `be' and the passive participle or participles. The existence of more than one passive participle in Esp-Ido creates some difficulties: what is exactly the difference between esas skribita and esis skribata, between esas skribota and esos skribata - in other words, should the time indication be added to the auxiliary or the main verb? There are here subtle shades of meaning which bewilder even clear-headed interlinguists. Further, does the combination esis skribita with its double indication of the past mean pluperfect, or can it be used as a translation of F a été écrit, because esis = `a été' and écrit generally = skribita (what has been written)? Couturat somewhere gives me esis konvinkita as a rendering of D ich bin überzeugt worden, but in another place writes "ta sistemo esis examenata e diskusata" with -ata, though it means practically the same tense.
All these systems are deficient, because they do no recognize the important distinction between a passive of becoming and a passive of being; the auxiliary which according to its original meaning applies only to the latter, is used also for the former, which indicates a change of state, while the passive of being denotes the state itself. (Cp. my Philos. of Grammar, pp. 272 ff. and Modern English Grammar, vol. iii, chs. xvii and xviii, especially p.389.) The languages mentioned above have the same usage, but there is in some of them a tendency to use a different auxiliary for the passive of becoming, E get (or become), I vengo. The distinction is carried through in D ich werde überzeugt and ich bin überzeugt, Dan jeg bliver (blir) overbeviist and jeg er overbeviist.
From the Scandinavian languages N takes the auxiliary bli (preterit blid for the passive of becoming, and combines it with the stem-form of the verb; the passive of being is naturally expressed by es and the passive participle.
We shall now proceed to examples which will show the importance of the distinction. Li porte non es klosat nun; lum bli klosa chaki vespre e sal anke bli klosa dis vespre the door is not shut now; it is closed every evening and will also be shut this evening. Me bli nultem konvikte per lon argumentes I am never (I never get) convinced by his arguments. Me es konviket ke lo es mentiere I am convinced that he is a liar. La es sepultet in Croydon; ob lan marito sal bli sepulte anke dar? She is (lies) buried at C.; is her husband also to be buried there? Lon libres blid venda in grandi nombre His books were sold in great numbers. Ti libre es vendat = ha bli venda. Tum kel non bli fa disdi, morge non es fat (morge non sal es fat): was heute nicht getan wird, ist morgen nicht getan. Li spenses kel non es pagat (kel non ha bli paga) sal bli paga in novembre.
With "non-conclusive" verbs (verbs which denote an activity that is not begun in order to be finished) the distinction is unimportant and we may say that bli ama = es amat, similarly with verbs like hate, praise, blame, admire, see, hear.
The participle in -t has up til now been called the passive participle, and that is its principal use. But there are cases in which it may be used as an active participle of the past (perfect), thus corresponding to Esp -inta. This may be justified by a reference to those verbs that are used both transitively and intransitively: chanjat, komensat, finat may mean both `that has been changed, begun, ended' and in analogy with these we may use morit = `dead' (that has died), li falat arbre the fallen tree, li pasat tempe (li pasatum) the past. But the cases where such forms are needed are not numerous. (D der gewesene soldat = ex-soldato.)