Learn Hardcore Spanish (Spain): Probablemente mi madre cuelgue este cuadro nuevo en el pasillo del fondo. - My mother will probably hang this new painting in the hallway at the back.

Because cuelgue is the present subjunctive, and probablemente expresses uncertainty / probability, which often triggers the subjunctive in Spanish.

With adverbs of doubt like probablemente, posiblemente, quizá, tal vez, you can usually use either:

Subjunctive → speaker sees it as uncertain, subjective
- Probablemente mi madre cuelgue este cuadro nuevo…
Indicative (future or present) → speaker presents it as more factual or confident
- Probablemente mi madre colgará este cuadro nuevo…
- Probablemente mi madre cuelga este cuadro nuevo… (more colloquial)

In your sentence, cuelgue emphasizes that it’s a possibility, not a firm prediction. Using colgará would sound like you’re more sure she will do it. Both are grammatically possible; the nuance is about degree of certainty and style (subjunctive is more careful/standard here, especially at the beginning of the sentence).

If cuelgue is present subjunctive, how can it refer to the future?

In Spanish, the present subjunctive very often refers to future events when they are:

uncertain
not yet realized
dependent on another idea (wish, doubt, condition, etc.)

Examples:

Cuando llegue mi madre, hablaremos.
→ When my mother arrives, we’ll talk.
Es posible que llueva mañana.
→ It’s possible that it will rain tomorrow.

So in:

Probablemente mi madre cuelgue este cuadro nuevo…

the verb is present subjunctive in form, but the context clearly places the action in the future (she hasn’t hung it yet). Spanish doesn’t need a special “future subjunctive” in everyday use; the present subjunctive does that job.

Could I say Probablemente mi madre cuelga este cuadro nuevo…? Is it wrong?

It’s not strictly wrong, but it sounds less natural in many contexts and more colloquial / regional.

More common options in standard Spanish would be:

Probablemente mi madre cuelgue este cuadro nuevo… (subjunctive – typical, especially in writing)
Probablemente mi madre colgará este cuadro nuevo… (future indicative – more confident prediction)

Using cuelga (present indicative) can happen in spoken Spanish, but:

it sounds more like a prediction stated as fact or a habitual behaviour
it is less clearly “future”; it could be interpreted as “that’s what she usually does”

For a learner, it’s safer and more idiomatic to use cuelgue or colgará here.

Where else can I put probablemente in the sentence? Does the word order change the meaning?

You can move probablemente around quite a bit:

Probablemente mi madre cuelgue este cuadro nuevo en el pasillo del fondo.
Mi madre probablemente cuelgue este cuadro nuevo en el pasillo del fondo.
Mi madre cuelgue probablemente este cuadro nuevo en el pasillo del fondo. (less common; more written/literary)

All of these are understandable. The basic meaning doesn’t change, but the emphasis does:

At the beginning (Probablemente mi madre…) you highlight the uncertainty.
After the subject (Mi madre probablemente…) sounds very natural and neutral in speech.

Also, when probablemente is at the beginning, Spanish tends to favour the subjunctive a bit more; in other positions, the indicative becomes more common, though both are possible depending on the speaker’s feeling of certainty.

What’s the difference between este cuadro nuevo and este nuevo cuadro?

The position of nuevo can slightly change the nuance:

este cuadro nuevo
- more literal: this new painting
- usually understood as new, as in not old / not used / recently acquired or painted
este nuevo cuadro
- often implies another / new addition, as in “this new painting (as opposed to the previous ones)”
- can sound more stylistic or emphatic

This pattern (adjective before vs. after the noun) is common with a few adjectives in Spanish:

un viejo amigo = an old friend (long-standing)
un amigo viejo = a friend who is old in age
un pobre hombre = a poor guy (to be pitied)
un hombre pobre = a man without money

In everyday conversation, este cuadro nuevo is the most straightforward way to say “this new painting.”

Why is it mi madre and not la mi madre (like in Italian or other languages)?

Spanish usually uses possessive adjectives (mi, tu, su, nuestro, etc.) without a definite article:

mi madre = my mother
mi hermano = my brother
mi casa = my house

Adding the article (la mi madre) sounds archaic, dialectal, or poetic in modern Spanish and is not standard.

So the normal, neutral way is mi madre, not la mi madre.

What exactly does del fondo mean in en el pasillo del fondo?

Del fondo is de + el fondo and here it means roughly:

“at the back” / “in the back” / “furthest back”

So:

el pasillo del fondo = the hallway at the back / the back corridor / the corridor at the far end

You’ll see del fondo in many similar expressions:

la habitación del fondo = the room at the back
la estantería del fondo = the shelf at the back
la mesa del fondo = the table at the back (e.g. in a café)

It gives a sense of farthest from the entrance or at the end of the space.

Why is it en el pasillo and not something like al pasillo or sobre el pasillo?

Because we’re talking about location, and Spanish typically uses en to mean “in / on / at” for places:

en el pasillo = in the hallway
en la pared = on the wall
en la mesa = on the table

Al pasillo would mean “to the hallway” (direction), not location. And sobre el pasillo would be “above the hallway”, which is not what we want.

So:

colgar algo en un sitio = to hang something in/on a place
→ cuelgue este cuadro nuevo en el pasillo del fondo = “hang this new painting in the back hallway.”

How would the sentence change if I were more certain, like “My mother will hang this new painting…”?

You’d normally switch to the future indicative (or sometimes the present indicative):

Mi madre colgará este cuadro nuevo en el pasillo del fondo.
→ clear future prediction, quite certain
Or, in some contexts (especially informal speech):
Mi madre cuelga este cuadro nuevo en el pasillo del fondo.
→ can be used as a scheduled / planned future

If you want to keep probablemente but sound more confident, you can say:

Probablemente mi madre colgará este cuadro nuevo en el pasillo del fondo.
(still “probably”, but phrased as a more straightforward prediction than cuelgue)

Is colgar always used for “to hang” objects like pictures?

Colgar is the normal verb for hanging things that are suspended from something:

colgar un cuadro = to hang a picture
colgar una lámpara = to hang a lamp
colgar la chaqueta = to hang up the jacket

But Spanish sometimes uses more specific verbs depending on the object:

tender la ropa = to hang out the clothes (to dry)
enganchar algo = to hook something on (a hook, a clip)
poner un cuadro can also be heard in casual speech for “put up a painting”, though colgar is more precise.

For a painting on a wall, colgar un cuadro is the safest, most natural choice.

Could I say en el pasillo de atrás instead of en el pasillo del fondo?

Yes, en el pasillo de atrás is understandable and also used, but there’s a slight nuance:

el pasillo del fondo → very idiomatic; suggests the corridor at the far end of a building or area.
el pasillo de atrás → more literally “the hallway at the back”; can imply a back hallway (e.g. near a back door), not necessarily at the far end of the main corridor.

In many real situations, both could refer to the same place, but el pasillo del fondo is a very standard way to say “the hallway at the far end.”