Good question. "lavarse" and "se lava" mean the same thing, but you have to use the lavarse construction when it immediately follows a preposition. So you could say either "(El) tiene que lavarse los manos" or "(El) necesita se lava los manos"
Another Example: Yo tengo que ducharme = I need to shower Debo me ducho = I must shower
Chris, you are partly right here. The verb form after a preposition must be the infinitive.
However, you've forgotten that the infinitive is used after a conjugated verb as well.
To correct your examples:
(Él) necesita lavarse las manos. He needs to wash his hands.
Debo ducharme. I must shower.
Are you saying that in Spanish the word "que" can be used as a preposition? Its translation, "that," is NOT an English preposition. Rather, "that" is an English demonstrative pronoun. Could you give an example of a sentence with a word that is a preposition in both Spanish and English, an example in which a reflexive construction like "lavarse" follows that preposition?
To answer Your fist question,' que' can be used as a preposition ( and i believe in this cases it is). You can't say 'que' always translate to 'that 'sometimes it translate to 'what'. The Spanish word 'que' does not translate well at all to English. Don't do word for word translation things like this mess you up.
So right, joseph_d_stein! Coming back to this page a year later, I would just like to add that, in my opinion, the Spanish word "que" is a particle in this sentence.
Particle definition: (in English) any of the class of words such as "in, up, off, over," etc., used with verbs to make phrasal verbs. Usually, it seems as though English particles of phrasal verbs are omitted in Spanish translations. Perhaps "que" is the exception because "has to" and "must" are both alternative translations of "tener + que."
Branden, the construction tener + que + infinitive is used to say what you have to do. Your se lava has to be in the infinitive form.
Spanish generally doesn't have two conjugated verbs together, and your sentence would be translated something like [He has to he washes his hands].
This rule often works in English, too:
Tengo que lavarme la cara. I have to wash my face.
Quiero estudiar. I want to study.
And sometimes the infinitive in Spanish doesn't translate to an infinitive in English:
Puedo ayudar. I can help.
Debo comer. I should eat.
Although "ayudar" and "comer" are infinitives, they can be translated into English gerunds, because in English both infinitives and gerunds can be used as noun substitutes.
However, if sentences like "Puedo ayudar" and "Debo comer" are translated using English gerunds, then sometimes it is necessary to use the subjunctive "be." Respectively, "I can be helping" and "I ought to be eating."
Just for the record, it should be noted that the English defective verb "ought" can be used to translate all of the different Spanish conjugations of "deber." "Ought" is the more old-fashioned, but still used, synonym for "should" in the voluntary sense.
If you want to translate "deber" in the coercive sense, then you use the English defective verb "must," as in "I must be eating" or "I must be helping." However, if you choose to use "must," it is more customary English to simplify, as in "I must eat" and I must help/I must be helpful." In these last sentences, "must" is used as a helping verb.
Lavar = to wash (clothes, car)
Lavarse = to wash oneself (one's hands, one's face)
Lavarse is a reflexive verb. The se on the end of the infinitive indicates that, and when you conjugate it you use the reflexive pronoun before the verb:
Me lavo las manos. I wash my hands.
Te lavas la cara. You wash your face.
Se lava los pies. He washes his feet.
Nos lavamos el pelo. We wash our hair.
Se lavan los codos. They wash their elbows.
Lavo mi coche los sábados. I wash my car on Saturdays.
Me lavo el pelo todos los días. I wash my hair every day.
Much more at studyspanish.com (Grammar Unit Five).
I've developed a technique for understanding the multiple verbs. Only one verb will be conjugated. If there is a second verb in the sentence it will be the infinitive form. I have to eat "Yo tengo que comer". Tengo is conjugated, comer is the infinitive. I can read; "Yo puedo leer". I do have trouble knowing whether the construction requires an extra article. Should it be Puedo leer, or Puedo a leer? Or does that depend on the application?
It depends on the verb and the application. There's no shortcut for these, you just have to memorize how each verb is used. There's an organized list at https://www.lawlessspanish.com/grammar/verbs/verbs-with-prepositions
To clarify, I wouldn't translate a sentence as "He has to wash her hands" unless that sentiment was specified in Spanish, as in "Él tiene que se lava las manos de ella."
What you need to understand, kbrady49, is that this is colloquial Spanish. In other words, whenever "las manos" follows a reflexive verb, "las manos" always means possessive pronoun + "manos." Another example is "Nos cepillamos los dientes." (We are brushing our teeth.)