Every day you do things for a reason. You go to the shop to buy milk. You call a friend to say hello. You save money to travel. English shows that reason with a tiny pattern: to plus a verb. If you do not know this pattern, your reasons come out broken, like 'I went the shop for buy milk.' People may still guess your meaning, but the sentence sounds wrong, and in an interview or an email it can make you look less confident than you really are.

The to-infinitive is also one of the busiest tools in English. It does not only give reasons. It follows verbs like want, need, plan, and decide ('I want to go'), it follows adjectives ('It is easy to learn'), and it shows results ('I woke up to find snow everywhere'). Learn this one small shape well, and suddenly hundreds of everyday sentences become easy to build.

First, the form. A to-infinitive is the word 'to' plus the base form of a verb: to eat, to work, to sleep. The base form never changes. Do not add -s, -ed, or -ing after 'to'. So we say 'to go', never 'to goes', 'to went', or 'to going'. This is true for every person and every time: 'She wants to go', 'They wanted to go', 'I will want to go'.

Second, the most common meaning: purpose. When you say why you do an action, put the to-infinitive after the action: 'I turned on the TV to watch the news.' The action is 'turned on the TV'; the reason is 'to watch the news'. Compare this with 'for'. With 'for', use a noun: 'I went out for bread.' With a verb, use 'to': 'I went out to buy bread.' Never say 'for buy bread'. That mix of 'for' plus a base verb is the classic mistake, and the fix is always the same: change 'for' to 'to'.

Third, the to-infinitive as a complement. A complement is just the part that completes another word. Many common verbs need a to-infinitive to finish their idea: want, need, hope, plan, decide, learn, try, agree, promise, offer, refuse. So we say 'I decided to stay', 'She hopes to pass the test', 'They agreed to help'. Some of these verbs also take a person before the infinitive: 'I asked him to wait', 'She told me to call her'. Adjectives work the same way: 'happy to help', 'hard to say', 'ready to order'.

Fourth, the to-infinitive for result. This use is smaller but useful. After certain patterns, the infinitive tells what happened next or what the outcome was: 'He grew up to become a doctor', 'I arrived home to find the door open', 'She is old enough to drive'. Notice the pattern 'enough + to-infinitive' and 'too + adjective + to-infinitive': 'too tired to cook' means the result is that you cannot cook.

Finally, negatives and questions. To make a to-infinitive negative, put 'not' before 'to': 'I decided not to go', 'He told me not to worry'. In questions, the pattern does not change: 'Why did you call? To ask a question?' You can even answer a 'why' question with just the infinitive: 'Why are you saving money?' 'To buy a car.'

1. 1. She went to the market to buy fresh vegetables.

   The to-infinitive 'to buy' gives the reason for going.

2. 2. I called the hotel to change my booking.

   Purpose after a phone action: to plus base verb 'change'.

3. 3. We stopped at a cafe to have some coffee.

   Travel context; 'to have' explains why we stopped.

4. 4. He is learning English to get a better job.

   A long-term goal expressed with 'to get'.

5. 5. Do you want to join us for dinner tonight?

   After 'want', use a to-infinitive, even in a question.

6. 6. I decided not to take the early train.

   Put 'not' before 'to' to make the infinitive negative.

7. 7. She promised to send the report before Friday.

   Work verb 'promise' is completed by 'to send'.

8. 8. It is easy to make soup at home.

   After an adjective like 'easy', use a to-infinitive.

9. 9. They saved money for a year to visit Japan.

   Money nouns take 'for'; the purpose verb takes 'to'.

10. 10. The doctor told me to drink more water.

    Pattern: tell + person + to-infinitive gives an instruction.

11. 11. I opened the window to let in some air.

    A home action followed by its purpose, 'to let'.

12. 12. He was too sick to go to work yesterday.

    'Too + adjective + to-infinitive' shows a blocked result.

13. 13. Are you ready to order, or do you need time?

    Adjective 'ready' plus 'to order' in a restaurant question.

14. 14. She woke up early to watch the sunrise.

    The infinitive 'to watch' answers the question 'why so early?'

15. 15. We need to check the weather before we leave.

    'Need' is completed by 'to check'; no 'for' anywhere.

The biggest mistake is using 'for' plus a verb to show purpose. Learners say 'I went the office for meet my manager' instead of 'I went to the office to meet my manager.' Why does the wrong version fail? In English, 'for' can only be followed by a noun or an -ing form in some fixed uses; it can never sit directly before a base verb. When your reason is an action, the only correct connector is 'to'. Also notice the missing 'to' before 'the office' in the wrong sentence — places you go to usually need 'to' as well.

A second common mistake is changing the verb after 'to'. Learners write 'She wants to goes home' or 'I planned to visited them.' Wrong: 'to goes', 'to visited'. Right: 'to go', 'to visit'. The word after 'to' is frozen in its base form. Time and person are shown by the first verb ('wants', 'planned'), never by the infinitive.

A third mistake is putting 'not' in the wrong place. Learners say 'I decided to not go' or 'He told me to don't worry.' The natural pattern is 'not' directly before 'to': 'I decided not to go', 'He told me not to worry.' 'Don't' belongs in normal negative sentences, not inside an infinitive.

• Reason is an action? Use 'to' + base verb, never 'for' + verb.
• The verb after 'to' never changes: to go, to eat, to work.
• Reason is a thing? Then 'for' + noun is fine: 'for bread'.
• Negative infinitive: 'not to' before the verb — 'decided not to go'.
• After want, need, plan, hope, decide, expect a to-infinitive.
• Answer 'Why?' with an infinitive: 'Why run? To stay healthy.'