The suffix fer- is very productive. It primarily takes verbs as input. The output is a transitive or ergative verb:

The verb prateto talk is inherently intransitive, whereas ferprate takes a direct object, i.e. syn tiidhis time in the example. In the example below, the ergativity of the verb ferreine is revealed by the auxiliary wêzeto be, here in the third person form is:

Frisian shows a further restriction when it comes to input of already prefixed verbs. In Dutch, this is possible to a certain extent, but it is excluded in Frisian. An example is Dutch veronderstellento suppose which is ûnderstelle in Frisian. Or take Dutch verontrustento alarm, where the corresponding Frisian word is ûntrestigje.

If the base form is a verb, the semantic contribution of fer- can quite generally be characterized as a movement, primarily away from a point, a form of a distancing, often in a sense that something gets lost. Examples that are in line with this very general interpretation are driuweto drive > ferdriuweto drive away, jeieto chase > ferjeieto chase awaysmiteto throw > fersmiteto reject.

Some more specific applications of the idea of distancing are:

• By some action of trade etc.: keapjeto buy > ferkeapjeto sell; hiereto hire (from someone) > ferhiereto rent (to someone); lotsjedraw lots > ferlotsjeto raffle off.
• By some form of loss: leareto learn > ferleareto forget (some skill). See also the opaque bases ferjitteto forget and ferliezeto lose.
• By some form of wasting: dobbeljeto dice > ferdobbeljeto dice away; dokterjeto be under medical treatment > ferdokterjelose money for medical treatment; dreameto dream > ferdreamewaste (one's time) by dreaming.
• By some form of damage denoted by the base verb: baarneto burn > ferbaarneto burn up; rotsjeto rot > ferrotsjeto disappear by rotting; sliteto wear > fersliteto wear out.
• By some form of damage created by too intensive use or action. The created verbs are usually reflexive. They denote that one finds oneself in an unwanted situation as a result of the action named in the base form. Some of the derivations denote that one exerts oneself physically or mentally as a result of the action named in the base form. Examples are iteto eat > jin feriteto overeat; feestjeto party > jin ferfeestjeto exert oneself in partying; swetseto blether > jin ferswetseto confound; rinneto walk > jin ferrinneto take the wrong turning; skreppeto grub > jin ferskreppeto strain oneself in grubbing. It should be noted that this category is remarkably more productive when compared with derivations with ver- in Dutch.
• By using up the base material implied by the base verb: bakketo bake > ferbakketo use by baking'; fuorjeto feed > ferfuorjeto use by feeding; tarreto live on > fertarreto spend.
• By causing something something to be no longer observable: bergjeto store > ferbergjeto hide; stopjeto put into > ferstopjeto conceal; swijeto be silent > ferswijeto keep silent about something.

Derivations with other verbal bases basically denote a change, comparable to what is going on with nominal or adjectival bases (see the section nouns or adjectives as base). The derivation can, for instance, refer to a change in form or substance, as in bouweto build > ferbouweto rebuild or klaaieto dress > ferklaaieto change clothes. More specifically, we see a replacement of old by new, as in fluorjeto construct a road > ferfluorjeto reconstruct a road.

There are, however, many fer-derivations with a verbal base that cannot easily be classified according to the categories above. Rather, they have an opaque meaning. Some examples are:

Base form	Derivation
spuieto spit	ferspuieto disdain
riedeto guess	ferriedeto betray
slaanto hit	ferslaanto defeat
moanjeto remind	fermoanjeto admonish
stjerreto die	ferstjerreto die
gunneto grant	fergunneto (be)grudge
drageto carry	ferdrageto bear

The prefix fer- can also take nouns and adjectives. In general, by prefixation some change is expressed, in principle in a causative or inchoative interpretation, although one of these possibilities may be suppressed for pragmatic reasons. With respect to base nouns, some important semantic sub-categories can be distinguished. The derivation may result in:

• Taking someone or something to another location: bêdbed > ferbêdzjeto bring (a patient) to another bed; heakhook > ferheakjeto hook up somewhere else; hûshouse > ferhúzjeto move.
• Covering something with the substance denoted by the noun: kopercopper > ferkoperjeto copper; nikkelnickel > fernikkeljeto nickel; sulversilver > fersulverjeto silver.
• Bringing about a change in form or substance inherent to the base noun: snipelsnippet > fersnipeljeto split up; stienstone > ferstienjeto petrify.

In the case of adjectival bases, the verbal derivation basically means 'making or getting A'. This process is quite productive. Some examples are:

Base	Derivation
amtlikofficial	feramtlikjeto bureaucratize
bitterbitter	ferbitterjeto embitter
bliidglad	ferbliidzjeto gladden
earmpoor	ferearmjeto become impoverished
frjemdstrange	ferfrjemdzjeto become estranged
ienfâldichsimple	ferienfâldigjeto simplify

There are a few cases where the stem is an adjective in the comparative degree, as recognized by the comparative suffix -er. Examples are ferâlderjeto age, ferbetterjeto improve, ferminderjeto worsen and ferwylderjeto run wild. This runs counter to the general tendency for inflectional morphology to appear outside rather than inside derivational morphology.

Some fer- verbs do not have a base form which occurs independently (anymore). Examples are listed below:

Base form	Derivation
*niele	fernieleto destroy
*kloffe	ferkloffeto sprain
*rêdzje	ferrêdzjeto almost fall apart by dryness
*dwine	ferdwineto disappear
*digenje	ferdigenjeto defend

In a few cases fer- coexisted with a variant oer-, and over time, the derivation with fer- became obsolete. Examples are listed below:

Base form	Derivation	Obsolete variant
winneto win	oerwinneto defeat	ferwinneto defeat
libjeto live	oerlibjeto survive	ferlibjeto survive
fuorjeto feed	oerfuorjeto overfeed	ferfuorjeto overfeed
*nachtnight	oernachtsjeto spend the night	fernachtsjeto spend the night

The phenomenon of replacing fer- by oer- can also be seen in the noun oergeunstenvy. Considering the verb fergunneto (be)grudge, one would expect the noun to start with fer-, but *fergeunst does not occur.

The prefix is pronounced as [fər]. However, the final segment /r/ is always deleted before a consonant, except before /h/, as is treated in Deletion of prefix-final /r/. Since the prefix contains a schwa, it never receives stress, e.g. ferGRIEmeto waste away, in line with the schwa restriction.