adverb
1
DUBIOUS : We started going out together just to have fun, as friends. Afterwards we both realized that there was more than just friendship.
GOOD : We started going out together just to have fun, as friends. Later on we both realized that there was more than just friendship.
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Afterwards suggests that the next thing happens as soon as the last thing has finished: 'On Saturday morning I went to see Adrian in hospital. Afterwards I drove into town to do some shopping.'
When there is a long interval or delay between two actions or events, use later on : 'I couldn't understand why she hadn't answered my letters. Later on I discovered that she had moved to a new address.'
2
DUBIOUS : First you draw a long straight line. Afterwards you draw another line, parallel to the first one.
GOOD : First you draw a long straight line. Then you draw another line, parallel to the first one.
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To introduce the next action in a process or series of actions, use then : 'Check that the paper is properly loaded. Then press the start button.'
Compare: 'We all had lunch together at one o'clock. Afterwards we went to the beach.'