• Tienen que acabar el trabajo para fines de Enero.
  They have to finish the work for the end of January.
• Hemos de seguir los consejos de los peritos en la materia.
  We have to follow the advice of those expert in the matter.

In such cases Tener is followed by que and Haber by de.[1] The former indicates compulsion or necessity, the latter a moral or self-imposed duty.

Haber de translates also "to be to,"[1] as:

• ¿Quién ha de hacer este viaje?
  Who is to go on this journey?

Tener de is used in threats:

• Tengo de llevarlo ante el tribunal.
  I shall take him before the court.

"Tener que hacer, que escribir, que comer" and similar expressions translate also "to have something to do, to write, to eat," as:

• Hoy tengo que hacer.
  To-day I have something to do, I am busy.
• Tengo mucho que hacer.
  I have much to do.
• Tenemos que comer por todo el día.
  We have something to eat which will suffice for the whole day.

Haber is used as a principal verb instead of Tener in:

• Haber menester de algo.
  To need something.
• He aquí el muchacho, etc.[2].
  Here is the boy (behold the boy here, etc.).
• Héme aquí or héteme[3] aquí, etc.
  Here I am (behold me here, etc.).

It also survives in some legal phrases, as:

• Fué habido el reo.
  The culprit was captured.
• Los hijos habidos en su primera mujer.
  The children by his first wife.

And in some idioms, as:

• Allá se las haya.
  That is his business.
• Habérselas con uno.
  To dispute with anybody.

Tener translates the English "to be" in such phrases as:

• Tener hambre, sed, sueño, calor, frío, vergüenza, and miedo.
  To be hungry, thirsty, sleepy, warm, cold, ashamed, and afraid.

Also speaking of age:

• Tengo veinte años.
  I am twenty years old.

• Tener razón.
  To be right.

And:

• No tener razón or Dejar de tener razón.
  To be wrong.

We said that the past participle when used with Tener agrees with the direct object, as:

• Tengo leídas las cartas.
  I have read the letters.

But when there is no direct object, of course the past participle remains invariable, as:

• Tengo entendido que....[4].
  I have heard that....