Pre-existing concepts 

Both are used to talk about inability, but they are used a bit differently.

can’t

👉 Negative form of can
👉 Used for general ability, possibility, or permission in the present

🔹 Very common and natural in everyday English
🔹 Short and informal

am not / isn’t / aren’t able to

👉 Negative form of be able to
👉 Used when you want to be more formal, more specific, or when can is not possible

🔹 Sounds more formal or neutral
🔹 Focuses on the situation, not just the ability

STEP 1: Check the tense

👉 Is the sentence in the present simple?

No (past, future, perfect) → use be able to

• • was / were able to

  • will be able to

  • haven’t been able to
    
    

Example:

• Yesterday, I ___ finish the exam.
  ✔️ wasn’t able to
  ❌ can’t (can is not used in the past)
  
  

STEP 2: Is it a general ability?

👉 Is it something that is always or usually true?

✔️ Use can’t

Examples:

• I ___ swim. → can’t

• She ___ drive. → can’t
  
  

STEP 3: Is it a specific or temporary situation?

👉 Is it about today, right now, this time, because of a reason?

✔️ Use am not / isn’t / aren’t able to

Examples:

• Today, I ___ come to class because I’m sick.
  → am not able to

• She ___ join the meeting this morning.
  → isn’t able to
  
  

STEP 4: Is the context formal or precise?

👉 In formal writing or exams:

✔️ be able to is often safer

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