These two words are often confused, just because they look so similar. They are related, but they are also quite distinct.

The first thing to notice is that affect is generally a verb, and effect is generally a noun. There is a noun affect (pronounced with the stress on the first syllable) but it is formal and rather infrequent; it refers to an emotion that changes what you do or think. The verb effect, pronounced the same as the noun, is also formal and means ‘to bring about’.

So the first way to distinguish between these two words is to see whether the one you are looking at is a verb or a noun. If it’s a verb, it almost certainly means ‘to change or influence something’. If it’s a noun, it probably means ‘a change produced in one person or thing by another’. You can see from this what the semantic link between the two words is: if something affects something else, it has an effect on it.

Here are some examples of affect and effect used in context:

Did the newspapers really affect the outcome of the election?
The disease affects (=has a bad effect on) many different organs of the body.
She had been deeply affected by her parents’ divorce.

Scientists are studying the chemical’s effect on the environment.
Any change in lifestyle will have an effect on your health.
East German companies were suffering the adverse effects of economic union.

In each of these example sentences, it is possible to replace the verb affect with a structure containing the noun effect and vice versa:

Did the newspapers really have an effect on the election?
Any change in lifestyle will affect your health.

First of all, Congratulations on your wonderful dictionary.

I would like to know what the difference is between the phoneme i and I, because I can't guess. Also I would like to know what the criteria is for you to use i or I to describe the phonetics of a word.

Example:
amiable (the phonetic transcription contains two types of i).

• /I/ (a capital ‘I’ but in smaller print) represents a short ‘i’ sound as in bit.
• /i/ represents a long ‘i’ sound as in bee. The colon-like symbol is a length mark.
• /i/ represents the ‘i’ sound at the end of pretty.

In fact, ‘short’ and ‘long’ are over-simplifications, and sometimes /I/ can actually be longer than /i/. But no matter how long you make the vowel sound in bit, it will never sound the same as the vowel sound in beat. This is because there is a difference in quality: for /i/, the tongue is further forward in the mouth than for /I/.

/i/ without the length mark is a sound with the same tongue position as /i/ but without the potential length. Unlike /I/ and
/i/, it only occurs in unstressed syllables.

Amiable is a slightly different case as it contains a diphthong. The first vowel sound is a sequence of /e/ followed by /I/, and so this sound is represented by the IPA symbol /eI/. The second vowel sound is the short ‘i’ sound, represented by IPA symbol /i/.

If you look at two other words on the same page as amiable you will see examples of the different ‘i’ sounds without the complicating factor of the diphthong. In American, the ‘i’ is short (IPA /I/). In amnesia the first ‘i’ sound is long and stressed (IPA /i/), and the second is short and unstressed (IPA /i/).