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in lesson 1.11 knowit you are very young. why cant you say, estas es muy joven

Estar and ser can be tricky for us English speakers. As you may know, the former is more of a temporary condition while the latter refers to something more permanent. I think it's something you have to get a feel for over time. Here are two examples taken from the same lesson: - ¡Tan grande que estas, mijito! - ¡Ya eres muy mayor para casarte!

Steven is right, sometimes when to use estar and when to use ser can be a bit fuzzy. In fact, occasionally the Peruvian girl that I study with once a week has to think a bit which is the most appropriate verb to use. Same thing with por and para. She knows instinctively which to use, but has to think why at times. I have had better luck thinking about estar and ser as a condition that is subject to change (estar) vs. an essential characteristic, what something is (ser.) Having said that, I know that the person will not always be young, but things that define what a person is in relatively long range are described by ser. More fluid descriptions likely to change more quickly are described by estar: estoy cansado...I am tired, but hopefully that condition will change once I have rested. In fact, I just realized that the word solid is a good way to think about ser, and fluid a good way to think about estar.

Generally speaking, I think of estar as either describing a temporary condition or used when stating where something is located. One uses ser to describe things that are more permanent. There are some sentences that will have significant different meanings depending on whether we use 'ser' or 'estar'. For instance: estoy aburrido = I'm bored soy aburrido = I am a bore estoy borracho = I am drunk soy borracho = I am a drunk Placement of the preposition 'a' can render quite different meanings in English. Consider "I am Danish" versus "I am a Danish".

"Ich bin ein Berliner!" "I am a jam doughnut!" - JFK at the Berlin wall, 1963. ;-)

Tu estas muy joven or tu eres muy joven. Usted esta muy joven or usted es muy joven. Yo estoy muy juven or yo soy muy joven. Nosotros estamos muy joven or nosotros somos muy joven. Ellos estan muy joven or ellos son muy joven. The verb ser sound so much better than the verb estar for this sentence.

That's actually a very good sign of progress in the language when phrases just sound right.

Just this morning I was thinking about how to say some things. In my mind I could see a junction ahead: will I need to use ser o estar, por o para? I took it as a good sign that I reached my decision before I got there. Then I was thinking that learning to speak a new language is a lot like learning to ride a mountain bike. At first you are focused on what is on the trail right ahead of your front tire and you fail to see big problems (rocks, roots, hairpin turns with steep dropoffs) that are approaching. As you get better you have the confidence to let your bike take care of the little things and look further ahead to see those bigger issues before it is too late. ¿Cómo es esa para una metáfora?

¡Bien dicho Dan!