Learners of English (and native English speakers too) often confuse these two words: Affect vs Effect. They also confuse forms of these words: Affectively vs Effectively; Affective vs Effective and so on.
Part of the problem is that they are pronounced almost the same: /əˈfekt/ and /ɪˈfekt/. Some English accents in fact will produce them exactly in the same way. Since they are often confused, this article explains what they mean and how to remember which one to use when.
Affect vs Effect
Affect with an a has a couple of meanings. The most common is as a verb meaning to influence emotionally.
The weather always affected his mood.
I can’t stop crying; her story affected me so much.
Sometimes affect with an a also means to act or pretend as in:
She affected a French accent.
On the other hand, effect with an e usually means the result of an action:
What was the effect of his speech? Did he manage to persuade them?
The CGI effects in this movie are incredible!
a useful mnemonic
So in the majority of cases, affect with an a is a verb while effect with an e is a noun and if you follow only one rule this will work most of the time and you’ll be right most of the time!
The mnemonic NEVA is useful here:
NEVA: noun effect; verb affect
Affective vs Effective
The difficulty here is that both these words are adjectives so they are grammatically used in the same way:
This is an affective speech.
This is an effective speech.
However, they do have slightly different meanings.
Affective means having an emotional influence while effective means producing a result. If you like, you can see these words as part of the same process:
an action > has an emotional influence > and produces a result
an action > is affective > and effective
So in the example of the speech above, it is affective because it influences people emotionally, and it is also effective because it produced the desired result, Suppose a presidential candidate gave a speech to persuade people to vote for them. A good speech would be affective because the crowd begins to cheer and clap. It would be effective if the crowd then went out and voted for the candidate.
Affectively vs Effectively
Again these words have the same grammatical use in that they are both adverbs and they describe how something happens. You need to look at the root meaning again to work out which one to use.
affectively = influencing emotionally
effectively = producing results
So take this example:
He speaks affectively.
He speaks effectively.
In the first case the speaker receives an emotional response from the audience. They begin to cry or cheer, etc. In the second example the speaker gets a good result from the crowd. They end up voting for him!