Creditoris interest fideiussorem adesse.

No. Here interest is not the English-style idea is interested.

It is the Latin verb interest from intersum, used impersonally, and it means things like:

• it matters
• it is important
• it is in the interest of
• it concerns

So Creditoris interest fideiussorem adesse means something like It is in the creditor’s interest that the surety be present, not The creditor is interested in the modern emotional sense.

Because the impersonal verb interest regularly takes the genitive of the person concerned.

So:

• creditoris interest = it matters to the creditor
• literally, something like it is of the creditor’s concern

This is one of those idiomatic constructions that you simply learn with the verb.

Also, creditoris is the genitive singular of creditor, creditoris.

An English speaker often expects a dative, because English says important to the creditor. But Latin does not follow English here.

With interest, Latin normally uses:

• genitive for a noun: creditoris interest
• special forms with some pronouns: mea interest, tua interest, nostra interest, etc.

So creditori interest would not be the normal classical way to say this.

Usually not in the same way.

With personal pronouns, Latin commonly uses forms like:

• mea interest = it matters to me
• tua interest = it matters to you
• nostra interest = it matters to us
• vestra interest = it matters to you all
• sua interest = it matters to him/her/them in a reflexive sense

So after seeing creditoris interest, it is useful to remember that pronouns are handled a little differently.

Because fideiussorem is the subject of the infinitive adesse.

In Latin, when a verb is in the infinitive and it has its own subject, that subject is very often put in the accusative. So:

• fideiussorem adesse = literally the surety to be present
• idiomatically that the surety be present

So fideiussorem is not the direct object of interest. It belongs with adesse.

Because Latin is expressing the content of what matters by means of an infinitive clause.

English often uses a that-clause:

• It matters that the surety is present

Latin very often uses an infinitive instead:

• fideiussorem adesse

So adesse is the present infinitive of adsum, meaning to be present.

It uses the same accusative + infinitive pattern that you know from indirect statement.

So for learning purposes, it is very helpful to recognize:

• fideiussorem = accusative subject
• adesse = infinitive

Strictly speaking, here it is just an infinitive clause depending on interest, not a report after a verb like say, think, or hear. But structurally it looks very similar.

Adesse is the present infinitive of adsum, adesse.

It usually means:

• to be present
• to be there
• sometimes to be at hand or to assist, depending on context

In this sentence, to be present is the natural sense.

No personal nominative subject appears, because interest is being used impersonally.

That means Latin does not say the creditor matters or anything like that. Instead, the construction is more like:

• it matters to the creditor
• that the surety be present

So the sentence is built around an impersonal verb plus a content clause.

A few natural translations are:

• It is in the creditor’s interest that the surety be present.
• It matters to the creditor that the surety be present.
• The creditor has an interest in the surety’s being present.

The important thing is not to turn interest into is interested. In this sentence, it means matters / is important.

Latin word order is flexible, but this order is very natural.

• Creditoris comes first to show immediately whose interest is involved.
• interest follows as the main impersonal verb.
• fideiussorem adesse stays together as the idea that matters: the surety to be present.

So the sentence is arranged in a clear way:

to the creditor / it matters / that the surety be present.

Latin could change the order for emphasis, but this version is straightforward and idiomatic.