5. Modal meanings

Importante
En esta sección vamos a repasar los verbos modales, simples y perfectos.
MODALES SIMPLES
Can, could, may, might, will, would, must, shall, should, ought to
Características
- Tienen una forma invariable y única, el infinitivo sin to: can, will, must...
- Realizan las preguntas usando la inversión, es decir, no necesitan ningún tipo de auxiliar: Can we dance?
- Siempre están seguidos de un infinitivo sin to del verbo que añade el significado: I can swim.
- Su función no es la de indicar un tiempo, sino una actitud o punto de vista del hablante.
Significado
- Probabilidad: se usan para decir cómo de seguros estamos de algo que ha sucedido, está sucediendo o sucederá.
It is snowing, so it must be very cold outside
(Está lloviendo, debe hacer mucho frío fuera)This can't be right, the bill is too high!
(Esto no puede estar bien, ¡la factura es demasiado alta!)
- Habilidad: para expresar lo que sabemos o no hacer.
I can swim very fast
(Sé nadar muy rápido)
- Obligación y consejo: para decir que algo es necesario o no, o para dar un consejo.
You must be here at seven
(Debes estar aquí a las siete)He should go to the doctor
(Deberías ir al médico)
- Permiso: para pedir o dar un permiso.
Can I open the window?
(¿Puedo abrir la ventana?)
- Prohibición, con mustn't y can't para decir que algo no está permitido.
You mustn't eat chewing gum in class
(No puedes comer chicle en clase)
You can't do that here
(No puedes hacer eso aquí)
Clasificación de verbos modales por su significado
- Posibilidad: can, could, may, might
- Obligación: should, ought to, must, have to
- Prohibición: don't have to, shouldn't, mustn't, can't
- Deducción positiva: have/has to
- Deducción negativa: can't
MODALES PERFECTOS
Se componen de un verbo modal + have + pasado de participio del verbo que añade el significado. Todos tiene un significado pasado, y expresan la actitud del hablante ante algo que ya ha ocurrido.
Aquí están los principales y su significado.
- Must + have + past parciple: expresa deducción en el pasado.
Jane is quiet today. She must have had some kind of trouble. (Jane está muy callada hoy. Debe de haber tenido algún tipo de problema.)
- Can't + have + past participle: imposibilidad o deducción negativa en el pasado.
Jake is an honest person. He can't have stolen that money.(Jake es una persona honesta. No es posible que haya robado ese dinero)
- Should (not) + have + past participle: expresa arrepentimiento sobre algo que se hizo mal en el pasado.
You should have apologized to him. (Debiste disculparte ante él)
You shouldn't have talked like that to the teacher.(No debiste hablar así al profesor)
También expresa probabilidad sobre algo que se esperaba que ocurriera y no estamos seguros de que realmente tuviera lugar.
They should have phoned by now, but I don't know if they are at home.
- Could + have + past participle: posible acción en el pasado que no se realizó por completo.
I could have bought that car but I didn't have enough money. (Pude comprar el coche pero no tuve suficiente dinero)
- May/might + have + past participle: posibilidad en el pasado
He might have arrived home. (Puede que haya llegado a casa)
- Needn't + have + past participle: expresa algo que se hizo y que no era necesario
You needn't have come. I feel better now. (No hacía falta venir/No tenías porque venir. Me encuentro mejor ahora)

Actividad de lectura
¿Qué conoces sobre volcanes? ¿Sabías que el Parque Nacional de Yellowstone podría erupcionar en un futuro no muy lejano? Lee este texto publicado en National Geographic y tradúcelo.
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The natural beauty of Yellowstone National Park may appear serene, but it's rooted in a violent volcanic past. Now, geologists have identified which parts of the park are most likely to erupt again someday.
Yellowstone's next major eruption will probably be centered in one of three parallel fault zones running north-northwest across the park, a new study predicts.
Two of these areas produced large lava flows the last time the supervolcano was active—174,000 to 70,000 years ago—while the third has had the most frequent tremors in recent years.
Knowing this will help scientists determine which areas of the vast park to monitor most carefully. The Yellowstone region is often referred to as a "supervolcano" because it has spewed more than 240 cubic miles (a thousand cubic kilometers) of ash and lava in a single event. The most recent of these massive blasts occurred some 640,000 years ago.
Smaller eruptions occur more frequently, said Girard, but the chance of one happening in any given year is still less than one in ten thousand. He described these eruptions as lava flows, which are not explosive: "They have very, very high viscosity and flow very, very slowly". Similar flows have fed the slow-growing lava dome at Mount St. Helens in the years after that volcano's major eruption, but Yellowstone's lava flows occur on a much grander scale.
"Some of these flows traveled up to 20 miles [32 kilometers]," said Girard, whose study appeared in the September issue of GSA Today. "We have never seen a rhyolite eruption of this magnitude in human history." By studying the titanium content of the lava flows, Girard's team determined that the source of these flows had risen very quickly from a magma chamber some 4 to 7 miles (6 to 12 kilometers) deep. The amount of titanium within the lava's quartz crystals marks the depth at which crystals formed out of the slowly cooling magma. So when the magma pauses at intermediate levels during its ascent, the titanium content of each crystal should vary from its center to its outer edges, like the layers of an onion.
But, Girard said, the crystals have no such features. This means that the magma rose quickly to the surface, without pausing long enough at any intermediate level for the crystals to grow.
"Quickly" in terms of geology, anyway. By human standards, the lava's rise was probably fairly slow, taking place over hundreds or thousands of years.
Does this relatively fast-moving magma suggest Yellowstone could soon have more eruptions?
"It is not an imminent hazard," Girard said. "Every study has concluded that there is no magma that is ready to erupt within any foreseeable future."
Ben Ellis, a volcanologist at the Institute of Geochemistry and Petrology, ETH Zurich, Switzerland, finds Girard's study "really neat" but notes that eruptive patterns can also change unexpectedly.
He referenced an older series of eruptions that initially occurred along a series of linear zones much like those found in Girard's study, but then "shifted abruptly to a new location outside of the linear zone."
Texto adaptado de National Geographic