Is "a" needed here?

[dawoodusmani]

Hi !
What's wrong with these sentences?
1- Keyboard looks like a typewriter.
2- Keyboard is an input device used for entering the data into the computer.

Someone told me that there should be "a" before each sentence (e.g.A keyboard) and there shouldn't be "the" before data. Are they right? I don't understand when I should use "a" with a countable noun and when not.
Regards!
Dawood

[aggelos]

And they were right. You need 'a' before 'keyboard' for the same reason you need it (and used it, too) before 'typewriter'. You must use 'a/an' before a countable noun in the singular number, when it's the first time you speak about something of which there are more than one and while it is still unknown which particular object you are referring to. Once we know which particular object we mean, we refer to it using 'the'.

In other words, you will almost always have to use 'a/an' before any one countable noun in the singular before it has become known. There are only a few cases when a singular countable noun can be used without an article before it, and these are mainly proverbial, as in "Put pen to paper". Also, you must not use 'the' before either countable nouns in the plural or uncountable nouns if they are still unspecified (not defined, not known yet). That's why you should not say 'the data' in your sentence: we don't mean any particular set of data that we know of, we mean any data that we may ever need to enter. We don't know what these are going to be, do we?

So, your sentences should read:
1- A keyboard looks like a typewriter. (All keyboards/any keyboard...)
2- A keyboard is an input device used for entering data (any data) into the computer.

[Tdol]

I would say:
A keyboard is an input device used for entering data into a computer.

I use the indefinite articles because I am not talking about any specific keyboard, etc. In scientific language, you will come across datum/data (sing/plural), but in common usage it is uncountable like 'information'. And in IT, I generally see it used uncountably. We wouldn't use the definite article because that would refer to specific data and you're talking about any data.

[dawoodusmani]

Thanks to both of you for your informative answer. But I've just developed some confusion that why, then, we use: "Mother is feeding her baby." " Father is drinking coffee." " Life is difficult." "Teacher will show you..."
Question: Why do we use these four coloured words without any article even though they are countable and they are introduced for the first time in the sentence.
Best regrads
Dawood

[aggelos]

There is a small number of words describing persons that are very close to us or we are with most of the time. The tendency for such words, not only in English but in other languages too, is to be used without any article at all. Mother and father, as well as grandpa, grandma and some more, belong to this group. You just learn when to use them without an article. Please note that when we speak of other people's mothers, fathers etc. this 'rule' does not apply.

Many words in English can be both countable and uncountable, depending on how and in what context they're used. In "Life is difficult" life is an uncountable noun: we speak of life in general, not an instance of a person or animal being alive. A life, on the other hand, is the life of one person or animal. Thus, we can say: "A war that took millions of lives", but we cannot say: "*Lives are difficult". Love is another word similarly used: "Love is a wonderful feeling" (uncountable); "A love that will never die" (countable).

[dawoodusmani]

Originally Posted by aggelos

There is a small number of words describing persons that are very close to us or we are with most of the time. The tendency for such words, not only in English but in other languages too, is to be used without any article at all. Mother and father, as well as grandpa, grandma and some more, belong to this group. You just learn when to use them without an article. Please note that when we speak of other people's mothers, fathers etc. this 'rule' does not apply.

Many words in English can be both countable and uncountable, depending on how and in what context they're used. In "Life is difficult" life is an uncountable noun: we speak of life in general, not an instance of a person or animal being alive. A life, on the other hand, is the life of one person or animal. Thus, we can say: "A war that took millions of lives", but we cannot say: "*Lives are difficult". Love is another word similarly used: "Love is a wonderful feeling" (uncountable); "A love that will never die" (countable).

Thank you aggelos. You've really been very helpful. Thank you dear Rechard you too.
Regards!
Dawood