Hola Paul,

Tengo que and necesito are pretty much interchangeable. When using tengo que we focus more on the "obligation" to do something and when using "necesito" more on the "need" to do something. 

I could say:

Tengo que trabajar. 

This implies the obligation to work.

or

Necesito trabajar. 

I need to work.

This implies the need to do it, because if you don't, you won't earn money and you won't be able to pay the rent etc. So someone with this in mind would probably use "necesito" instead of "tengo que".

I would add that "tengo que" is more commonly used than "necesito", as the latter sounds a bit more formal.

Saludos

Inma

Hola Louie

With modal verbs we don't conjugate the main verb that comes after. You always need the infinitive.

What you need to conjugate is the modal/auxiliary verb.

Saludos

Inma

Hola Nicole

I am copying here what I replied to Alex (the answer was on a different thread):

For the first one "I didn't need to have an interview" we would say: 

It is very straight forward in this case.

However, for the second one "I needn't have cooked dinner" we would either say:

or

This way you get the meaning of something you did but it wasn't necessary in the end.

I hope this helps.

Inma

Hi Alexander,

Could you give me a bit of context so I can be more accurate in my reply please?

Inma