Iudex non dubitat quin mercator amicum fallere conatus sit.

After expressions of doubting or not doubting, Latin often uses quin plus the subjunctive.

So:

• non dubitat quin ... = he does not doubt that ...
• literally, he does not doubt but that ...

This is a very common pattern. A learner may expect quod or an accusative-and-infinitive construction, but with non dubitare Latin regularly prefers quin.

So in this sentence:

• Iudex non dubitat quin ...
  = The judge does not doubt that ...

Because quin introduces a subordinate clause that normally takes the subjunctive.

Here the verb is:

• sit = present subjunctive of sum

But it is not standing alone. It is part of the perfect infinitive idea formed with conatus sit, which means has tried or, in smoother English here, tried.

So the subjunctive is not mainly about uncertainty in English terms; it is there because the grammar of quin requires it.

Conatus sit is the perfect subjunctive of conor, conari, conatus sum, meaning to try or attempt.

Since conor is a deponent verb, it looks passive in form but has an active meaning.

So:

• conatus = perfect participle form
• sit = subjunctive of sum
• together, conatus sit = he has tried / he tried

Because the subject is mercator and that noun is masculine singular, the participle is also masculine singular: conatus.

A deponent verb is a verb that uses passive-looking forms but has an active meaning.

So although conatus may look like a passive participle to a beginner, it does not mean having been tried. It means having tried.

For example:

• conatur = he tries
• conatus est = he tried / he has tried

In this sentence:

• mercator ... conatus sit = the merchant has tried / the merchant tried

So you should translate it actively, not passively.

The merchant is doing the trying, and the friend is the person the merchant tried to deceive.

Here is the grammar:

• mercator = nominative singular, so it is the subject of conatus sit
• amicum = accusative singular, so it is the object of fallere
• fallere = to deceive

So:

• mercator amicum fallere conatus sit
  = the merchant tried to deceive his friend / a friend

Because it depends on conatus sit.

Latin uses an infinitive after verbs like conor to express what someone tries to do.

So:

• fallere conatus sit = has tried to deceive
• literally, has tried to deceive

This is similar to English:

• He tried to deceive his friend.

So fallere names the action attempted by the merchant.

Because fallere takes a direct object, and amicum is the direct object.

• fallere = to deceive
• whom did he try to deceive? amicum

Therefore amicum is in the accusative case.

A learner might also wonder whether amicum could belong with iudex somehow, but grammatically it goes with fallere, not with iudex.

Formally, conatus sit is perfect subjunctive. In English, the best translation depends on context:

• has tried
• tried

In a sentence like this, English often prefers simple past:

• The judge does not doubt that the merchant tried to deceive his friend.

But has tried is also possible if the context emphasizes a completed action with present relevance.

The important point is that the action of trying is viewed as completed.

Because the two verbs express different times or aspects.

• dubitat = the judge does not doubt now
• conatus sit = the merchant tried / has tried earlier, as a completed action

Latin often combines a present main verb with a perfect subjunctive in a subordinate clause when the subordinate action is prior or complete relative to the main idea.

So the sense is:

• The judge does not doubt now that the merchant previously tried to deceive his friend.

It is flexible, but not unusual for Latin.

The sentence is:

• Iudex non dubitat quin mercator amicum fallere conatus sit.

A more English-like order might be:

• Iudex non dubitat quin mercator conatus sit amicum fallere.

But Latin often places words for emphasis or rhythm rather than keeping a fixed subject-verb-object order.

The roles are still clear because of the endings:

• iudex = subject of dubitat
• mercator = subject of conatus sit
• amicum = object of fallere

So even if the order feels freer than English, the grammar tells you how the words fit together.

Yes, quin can sometimes have other uses, including expressions like quin? meaning something like why not?

But here it is part of a fixed construction after non dubitat. In this context, it means that in the sense of that ... not not, or more literally but that.

So you should read:

• non dubitat quin ... = does not doubt that ...

not as a separate adverb or question word.

Context and construction tell you which meaning is intended.