Pensavo che il tassista conoscesse già quella deviazione, ma ha dovuto controllare la mappa.

Pensavo is the imperfetto, and it often describes a mental state, background thought, or ongoing assumption in the past.

Here, Pensavo che... means something like:

• I was thinking that...
• I thought...
• I assumed...

It sets up the speaker’s expectation before the later event happened.

If you said ho pensato, it would sound more like a completed, specific act of thinking:

• Ho pensato che... = I thought / it occurred to me that...

That is possible in some contexts, but pensavo fits better here because it describes the speaker’s prior belief, which is then contradicted by ma ha dovuto controllare la mappa.

Because after pensavo che, Italian normally uses the subjunctive.

So:

• pensavo che
  • conoscesse

This is the imperfetto del congiuntivo.

Why? Because the sentence expresses what the speaker believed or assumed, not a simple fact being stated directly. In Italian, verbs like pensare, credere, supporre, and similar expressions often trigger the subjunctive after che.

So:

• Pensavo che il tassista conoscesse... = I thought the taxi driver knew...

Using conosceva here would sound nonstandard in careful Italian, because after pensavo che the expected form is the subjunctive, not the indicative.

This is due to the normal sequence of tenses in Italian.

The main verb is in the past:

• Pensavo

So the subordinate verb usually shifts into a past-form subjunctive:

• che ... conoscesse

A very useful pattern is:

• Penso che sia = I think that he/she is
• Pensavo che fosse = I thought that he/she was

And similarly:

• Penso che conosca = I think he knows
• Pensavo che conoscesse = I thought he knew

So conoscesse matches the past point of view introduced by pensavo.

Ha dovuto presents the action as a concrete event that actually happened:

• he had to check the map
• he ended up needing to check the map

It moves the story forward.

By contrast, doveva can mean:

• he was supposed to
• he had to / needed to in a more ongoing or descriptive sense

In this sentence, the speaker is contrasting expectation and reality:

• I thought he knew the detour already,
• but then he had to check the map

That makes ha dovuto the natural choice, because it refers to the specific completed situation.

Già means already.

So:

• conoscesse già quella deviazione = already knew that detour

Its position is flexible, but già is often placed before the element it modifies most clearly.

Here it highlights that the speaker expected the taxi driver to know the detour beforehand, without needing to check anything.

Possible placements include:

• conoscesse già quella deviazione
• già conoscesse quella deviazione

The first version is very natural and common.

Quella means that and points to a specific detour, presumably one already understood from the situation.

So:

• la deviazione = the detour
• quella deviazione = that detour / that particular detour

Using quella makes it feel more specific and identifiable, as if speaker and listener both know which route change is being talked about.

In English, we often do the same:

• I thought he already knew that detour

In Italian, conoscere is used for being familiar with people, places, routes, or things through experience.

Here the idea is not just knowing a fact, but being familiar with a route or detour.

So:

• conoscere una strada
• conoscere una zona
• conoscere una deviazione

all make sense.

By contrast, sapere is more about knowing information or how to do something:

• so la risposta = I know the answer
• so guidare = I know how to drive

So conoscesse quella deviazione means the driver was expected to be familiar with that detour.

Italian often uses the definite article where English would not, especially when referring to a specific person in a role or profession.

So:

• il tassista = the taxi driver

In context, this means the taxi driver we are talking about, probably the one driving the speaker.

English could also say:

• I thought the taxi driver already knew that detour

Italian strongly prefers the article here.

Often yes, but the exact nuance depends on context.

Deviazione can mean:

• a diversion
• a detour
• a route that has been changed, often because of roadworks, traffic, or a blockage

So in a driving context, quella deviazione is very naturally understood as that detour or that diversion.

A native speaker may choose the best English word from context, but detour is a very good translation here.

Yes, it is natural.

Controllare la mappa means:

• to check the map

It suggests looking at the map to confirm the route.

Other possibilities exist, with slightly different shades of meaning:

• guardare la mappa = look at the map
• consultare la mappa = consult the map
• verificare sulla mappa = check on the map

But ha dovuto controllare la mappa is perfectly normal and idiomatic.

Yes, Italian has some flexibility in word order, though the original sentence is very natural.

For example, you could also hear:

• Pensavo che il tassista conoscesse già quella deviazione, ma ha dovuto controllare la mappa.
• Pensavo che il tassista già conoscesse quella deviazione, ma ha dovuto controllare la mappa.

Both work.

However, the original order is clear and smooth because:

• Pensavo che... introduces the expectation
• ma... introduces the contrast
• già sits in a natural position before quella deviazione

So while word order can vary, the given version is a strong standard choice.