Some Commonly Confused Constructions

[Ser vs Estar] [Use of Estar] [Use of Ser] [Summary] [Saber vs Conocer] [Use of Saber] [Use of Conocer]
[Por vs Para]* [Object Pronouns -- Direct, Indirect and Reflexive ] [Demonstrative Adjectives and Pronouns]*

Ser vs Estar Use of Estar

A	To tell location.	El libro está en la mesa.
B	To describe health.	Estoy muy bien.
C	With adjectives to describe conditions.	Estoy muy ocupado.
D	In a number of fixed expressions.	Estoy de acuerdo. Está bien.
E	To form present participle.	Estoy estudiando ahora mismo.

Use of Ser

A	To identify people and things.	Yo soy estudiante. Esto es un libro. Alicia y yo somos amigos.
B	To express nationality; with de to express origin	Son cubanos. Son de la Habana. ¿De donde es Ud?
C	With de to express of what material is something made	Este bolígrafo es de plástico
D	With para to tell for whom or what is something intended	Es para la clase de inglés. Es regalo es para Sara.
E	To tell time.	Son las once. Es la una y media.
F	With de to express possesion.	Es de Carlota.
G	With adjectives to describe basic, inherent qualities or characteristics of people and things.	Soy sentimental. El coche es muy viejo.
H	To express generalizations (only with es)	Es importante estudiar, pero no es necesario estudiar todos los días.
!!!	de + el = del	Es la casa de la profesora. Es la casa del profesor.

The main difference is that estar refers to temporary attributes while ser to permanent or more lasting ones.
The best way would be to think of estar as of spanish version of present continuous or a word being:
The book is being on the table. I am being well. She is being busy.

Also note that "estar aburrido" means "to be bored", BUT!!! "ser aburrido" means "to be boring".

Saber vs Conocer Use of Saber

A	To indicate knowledge of facts or pieces of information.	Ud. sabe su número de teléfono, ¿verdad?.
B	To know how to do something.	¿Sabes jugar al ajedrez?

Use of Conocer

A	To know (be acquainted) with a person, place, or thing.	Conozco un buen restaurante cerca de aquí.
B	To meet.	¿Quieres conocer al nuevo profesor?

NOTE! Saber and conocer change their meaning whens used in preterite -- see the list of meanings for these and some other verbs.

Por vs Para

Por:

by, by means of	Vinieron por avión.
through, along	Me gusta pasear por el parque y por la playa.
because of, due to	Estiy nervioso por la entrevista.
during, in (time of day)	Trabajo por la mañana.
for = in exchange for	Piden 1.000 dólares por el coche.
for = for a period of time (often omitted)	Jugaron por tres horas.
for = for the sake of, on behalf of	Lo hago por ti.

Por is also used in a number of fixed expressions, such as:

por Dios
por ejemplo
por eso
por favor
por fin
por lo general
por lo menos
por primera/última vez
por si acaso
¡por supuesto!

for heaven's sake
for example
that's why
please
finally
generally, in general
at least
for the first/last time
just in case
of course!

Para:

in order to + infinitive	Para ganar, hay que practicar.
for = destined for, to be given to	Todo esto es para ti.
for = by (deadline)	Tendremos los resultados para mañana.
for = toward, in the direction of	Salieron para Lima.
for = to be used for	Es un vaso para agua.
for = in one's opinion, compared to others	Para mí, el español es fácil.
for = in the employ of	Trabajan para el gobierno.

Overall, para always has the underlying purpose of referring to a goal or destination.

Object Pronouns -- Direct, Indirect and Reflexive

The only possibly confused ones are 3rd person pronouns. They are lo/la/los/las (direct), le/les (indirect), and se (reflexive). The rest is the same -- me, te, nos, os.
Direct pronouns answer the questions ¿qué? and ¿quién? (what? and who?), while indirect ones answer the question ¿a quién? (for whom? and to whom?).
Reflexive pronouns show that the person doing action is the person who the action is directed at. Indirect pronouns are in fact identical to reflexive ones -- except that the recipient of the action is different from its performer.
Direct pronoun lo can also refer to actions, situations or ideas in general. In such a case it expresses English it or that.
For a full list of pronouns, click here. Also see expressing likes and dislikes.

Placement (comparative scale): One gets easily lost in different prepositions, especially when there is more than one and when it is not clear right away which is what. This table describes a placement order (whether in front of a verb or after), which cannot be reversed. It's a shame many textbooks skip it!

te
os

me
nos

le
les

lo/la
los/las

Note that (see below for details):

reflexive pronoun always comes first;
indirect pronoun always preceds direct one;
se always comes first;
te/os always precedes all the rest;
me/nos always comes before l- pronouns;
se in the beginning can be reflexive or indirect, as well as impersonal or passive (click here for more information on se);
me/nos as well as te/os can be indirect, direct or reflexive.

Examples

Te lo dijo.
Se lo entregaron.
No te me pongas dificil!
Me lo enseñó.
Se te dijo.
Quiero regalártelo.

He told you that.
They delivered it to you.
Don't get difficult 'on me'! (negative command)
He taught me how to do it.
It was said to you. (passive se)
I want to present it to you. (infinitive)

Placement (one pronoun -- direct, indirect, reflexive):

(After no) and before conjugated verb:	Lo hice el lunes pasado. No te presto el coche. Me ducho todos las tardes.
After no and before negative command:	No lo lea Ud. No me dé su número de teléfono ahora. No se siente.
After and attached to an infinitive:	Voy a hacerlo el lunes. Voy a guardarte el asiento. Tengo que ducharme mañana.
After and attached to an affirmative command:	Léalo, por favor. Sírvanos un café, por favor. Siéntose, por favor.
After and attached to a present participle:	Estoy comiendolo. Estoy escribiendole a una carta a Marisol. Pablo está bañándose.

Placement (two pronouns):

When there are both direct and indirect pronouns, the order is ID -- indirect / direct and nothing should come between them. Reflexive pronoun always comes first. The rules for placement with respect to the verb remain the same.	Te lo preparo ahora mismo. Sí, acaban de dármelo.
When both pronouns begin with l, indirect pronoun le/les becomes se.	Le compra unos zapatos. --> Se los compra.

When pronouns are being attached to a verb (present participle or affirmative command), it is necessary to add accents over the stressed sylllable to maintain the pronunciation:

Pablo se está bañando.
Lea el texto, por favor.

Pablo está bañándose.
Léalo, por favor.

When one pronoun only is being attached to an infinitive there is no need for an accent. Since an infinitve ends in r, the stress falls on the last syllable. When a pronoun is attached, the stress will fall on the next-to-the-last syllable (i.e. the same as before), since all pronouns are monosyllables and end either in a vowel or in s (for accents click here).

Le quiero hablar.
Lo tengo que escribir.

Quiero hablarle.
Tengo que escribirlo.

When the indirect pronoun is me, te or nos, only the pronoun is used. Adding a mí, a ti or a nos would be over-emphatic.

Mama me compró un carro.
Mama me compró un carro a mí.
Mama compró un carro a mí. BUT!!! Mama compró un carro.

Correct.
Over-emphatic.
Incorrect -- me is missing. Correct -- there is no
emphasis on for whom the car is bought.

When the indirect object is le (or se), either the pronoun only or the pronoun and the noun are used. Adding the noun or pronoun object of preposition is often necessary to clarify the meaning, since le/se may correspond to to/for you (formal -- singular or plural), him, her, them.

Mama le compró un carro.
Mama le compró un carro a Oscar.
Mama les compró un carro a Oscar y Julia.
Se las doy a Ud./él/ella/Uds./ellos/ellas.

When two pronouns are present and the direct one is the first or second person, then prepositional form is used for the indirect pronoun.

Me presentó a ella. NOT!!! Le me presentó.
Nos envió a Ud. NOT!!! Le nos envió.

That however, is not the case for the commands: No te me pongas dificil!

Demonstrative Adjectives and Pronouns

Adjectives:

Singular Masculine	Singular Feminine	English Equivalents	Plural Masculine	Plural Feminine	English Equivalents
este ese aquel	esta esa aquella	this that that...over there	estos esos aquellos	estas esas aquellas	these those those ...over there

Pronouns:

Singular Masculine	Singular Feminine	English Equivalents	Plural Masculine	Plural Feminine	English Equivalents
éste ése aquél	ésta ésa aquélla	this that that...over there	éstos ésos aquéllos	éstas ésas aquéllas	these those those...over there

Also, esto, eso and aquello are used to refer to statements, abstract ideas, or things that have not been identified. They are of a neuter form, have no plurals or accented forms.

In English, the world is divided into two groups -- this/these which refer to things close to a speaker, and that/those, which refer to things far from a speaker. In Spanish, the world is divided into three groups -- este/estos/... (with plurals and accented forms), which refer to things close to a speaker, ese/esos/..., which refer to things close or relating to a person spoken to, and aquel/aquellos/..., which refer to things far from both.