The importance of conjunction A in Russian

For those of you who have been learning Russian for quite some time, it wouldn’t come as a surprise that, besides the common conjunctions И (and) and НО (but), there is another one that is essential to everyday speech and to the language in general. This conjunction is А.
It falls right in between the “and” and “but” category in English, and is commonly translated as one or the other.
Modern grammarians argue that the use of A in speech is related to the level of the language awareness, suggesting that more competent speakers tend to use it more flexibly.

Here are the main differences in the meanings of the three conjunctions (which you can use as a note to yourself later on in your studies):

И (and) is all about COMBINING and MERGING things, SIMULTANEOUS ACTIONS;

Отец сидел и смотрел, как дети играют в мяч.
Шёл дождь, и был сильный ветер.

НО (but) is associated with CONFLICT and OBJECTIONS / PROTESTS, shows a NEGATIVE ATTITUDE toward the information;

Светило солнце, но было холодно.
Уже было поздно, но гости не хотели уходить.

A (and/but) implies CONTRASTS or SHIFT OF FOCUS from ONE object to ANOTHER;

Его отец работает в Москве, a мать – в Киеве. (and – shift of focus)
Я люблю красный цвет, а синий мне совсем не нравится. (but – contast)

The conjunction A can be used with HE to oppose actions, objects, implying that there is something unexpected in one of the parts of a sentence. In this case it would be translated as “but” in English. НО wouldn’t work here because it indicates contradiction, while all we need is clarification of some sort.

Она купила не груши, а яблоки.

It is also widely used in dialogues and serves as a return question or a link between interlocutors’ utterances (mainly used to change focus from one speaker to another) or as a sentence opener (a question opener):

– Где Вы работаете?
– Я преподаю в университете. А Вы?
А я – менеджер по продажам.

– Как дела?
– Отлично! А у тебя?
– Неплохо.

А что ты делаешь завтра вечером, Оля?
– Завтра я иду в кино с подругами. А что?
– Ничего. Я думал пригласить тебя в театр. Тогда в другой раз.

The last one is a particularly important pragmatic function of A that makes the speech, especially the colloquial speech, more cohesive, linked and true to how Russian speakers actually talk.