Learn Hardcore Spanish (Spain): No pienso que el contrato sea perfecto, pero es un buen comienzo. - I do not think the contract is perfect, but it is a good start.

Pienso que el contrato es perfecto.
→ I think the contract is perfect. (speaker believes it) → indicative (es)
No pienso que el contrato sea perfecto.
→ I don’t think the contract is perfect. (speaker does not believe it) → subjunctive (sea)

Negating pensar que (or creer que, opinar que, etc.) usually switches the verb in the subordinate clause to the subjunctive in standard Spanish grammar.

Would No pienso que el contrato es perfecto be completely wrong?

It’s considered non‑standard / incorrect in careful or formal Spanish, especially in Spain.

Native speakers in some regions do say it in fast or informal speech, but grammar rules (and what you should learn for exams or formal writing) clearly prefer:

No pienso que el contrato sea perfecto.

So you’ll be understood with es, but it will sound off or careless to many speakers, and teachers will normally mark it as wrong.

Why does No pienso que… use the subjunctive, but Pienso que… uses the indicative?

Because the meaning changes from belief to non‑belief:

Pienso que… = I think / I believe that…
→ the speaker affirms something → indicative:
Pienso que el contrato es perfecto.
No pienso que… = I don’t think that…
→ the speaker denies or doubts it → subjunctive:
No pienso que el contrato sea perfecto.

Same pattern with other verbs of opinion:

Creo que vendrá. → indicative or future as normal
No creo que venga. → subjunctive (venga)

Could I say Pienso que el contrato no es perfecto instead? What’s the difference?

Yes, that is perfectly correct:

Pienso que el contrato no es perfecto.
= I think the contract is not perfect.

Both sentences are grammatical, but there’s a slight nuance:

No pienso que el contrato sea perfecto.
Focus on denying the idea “the contract is perfect”. It feels like you’re reacting to, or distancing yourself from, someone else’s claim.
Pienso que el contrato no es perfecto.
Focus on stating your own opinion that it’s not perfect, more neutral and direct.

In everyday conversation they’re usually understood as the same idea, but stylistically they’re a bit different.

Why is it sea perfecto (with ser) and not esté perfecto (with estar)?

Because perfecto here describes an inherent or overall quality of the contract, not a temporary state.

ser + adjective → essential characteristics, general evaluations
- El contrato es perfecto. (in general, as a quality)
- El coche es caro. (by nature, as priced)
estar + adjective → temporary state, current condition
- El contrato está firmado. (state after being signed)
- El coche está sucio. (right now)

Saying No pienso que el contrato esté perfecto would sound odd; estar perfecto is used more with things like food, arrangements, or something being “just right” at that moment (e.g. La carne está perfecta).

Why is it el contrato and not just contrato?

Spanish uses the definite article (el, la, los, las) more often than English when we refer to a specific thing.

Here, you are talking about a particular contract (for example, the one on the table, or the one you’re negotiating), so Spanish uses:

el contrato = the contract (this specific one)

If you left the article off (No pienso que contrato sea perfecto), it would be ungrammatical in this sentence. You basically always need el before contrato here.

Why is it un buen comienzo and not un bien comienzo?

Because:

bueno / buen is an adjective = good
bien is an adverb = well

You need an adjective to describe comienzo (a noun), so you use bueno.

Before a masculine singular noun, bueno normally shortens to buen:

un buen comienzo = a good start
un buen libro = a good book
un libro bueno (also possible, slightly different emphasis)

un bien comienzo is incorrect, because bien cannot modify nouns.

Why is it buen and not bueno in un buen comienzo?

Bueno has a shortened form buen that’s used before masculine singular nouns:

un buen comienzo
un buen día
un buen contrato

After the noun (or with feminine / plural nouns), you use the full form:

un comienzo bueno (less common, a bit more emphatic)
una buena idea
unos buenos contratos

So un buen comienzo is simply the normal, idiomatic position and shortened form.

Why is it pero and not sino?

Because the second part doesn’t correct the first; it simply adds a contrast.

pero = but / however — adds a contrasting idea
sino = but rather — replaces or corrects the previous idea, usually after no

In your sentence:

No pienso que el contrato sea perfecto, pero es un buen comienzo.
= I don’t think the contract is perfect, but it’s a good start.
You’re not correcting “not perfect”; you’re adding that, despite its imperfections, it’s still a good start.

Compare with a typical sino structure:

No es perfecto, sino aceptable.
= It’s not perfect, but rather acceptable. (correcting the idea)

Why is the no placed before pienso instead of before sea?

In Spanish, no normally goes directly before the conjugated verb it negates.

Here, what you’re negating is pienso (I think), not sea:

No pienso que el contrato sea perfecto.
= I don’t think (that) the contract is perfect.

If you said Pienso que el contrato no sea perfecto, it would be strange and unnatural; Spanish almost never negates the verb inside a subjunctive clause like that in this particular structure. You would instead say:

Pienso que el contrato no es perfecto. (indicative, different structure)

What’s the difference between pensar que and pensar en? Could I say No pienso en que el contrato sea perfecto?

They’re different:

pensar que + clause = to think that… (opinion)
- Pienso que el contrato es justo.
- No pienso que el contrato sea perfecto.
pensar en + noun / idea = to think about… (have in mind)
- Pienso en el contrato. = I’m thinking about the contract.
- Pienso en ti. = I’m thinking about you.

No pienso en que el contrato sea perfecto is grammatically possible but sounds odd and unnatural in this context. For opinions you should use pensar que, as in the original sentence.

Could I use creo instead of pienso? Does it change the grammar?

You can, and the grammar pattern stays the same:

Creo que el contrato es perfecto. (affirmative → indicative)
No creo que el contrato sea perfecto. (negative → subjunctive)

Creo and pienso are very close in meaning here (I believe / I think). In everyday speech in Spain, creo que… is probably more frequent than pienso que…, but both are natural in this sentence.