Difference between 'decline' and 'decrease'

Question

I have an advanced English student who is stuck on the word 'decline'. I told him 'decline' and 'decrease' are very similar, but are not always interchangeable. It is a business English course and we were talking about what Customer Focus means. I wanted him to say "A company needs to decrease its customer base in order to increase Customer Focus". And instead he used "decline its customer base", which is not correct (right?!).

He then used the example of "stocks declining in the last quarter" to prove that you could use 'decline' to mean 'decrease'.

Does anyone have a good rule or way of explaining when to use 'decline' vs. 'decrease'?

Answer 1

When decline is used as a transitive verb, it means "to refuse" or "to say no to": We are declining your loan application. - I regret that I must decline your invitation. Declining a customer would be a bad business move; declining your customer base is simply ungrammatical. Probably bad business too.

When a sentient actor (a person, a corporation, an intelligent animal) is the subject of decline in an apparently intransitive sense, there is generally an implied object; I would call this a "virtually transitive" use: I offered him a job, but he declined (the job). - We offered the chimp a banana, but she declined (the banana).

When a non-sentient noun is used as the subject of decline, it means that that thing/resource/quality is becoming less, or less powerful: The puma population has been declining for the past few years. - Hari Seldon says that the Empire is declining.

When a thing is declining, or a person's health or power is declining, we can say that that thing or person is in decline. As soon as his team started losing, he went into a decline. - This country's been in decline ever since they raised the drinking age.

When decrease is used as a transitive verb, it means "to reduce the amount of": I'll have to decrease my donut intake, or else my chair will break.

Sentient actors don't decrease intransitively; you can't say He decreased.

When a non-sentient noun is used as the subject of decrease, it means that that thing/resource/quality is becoming less: The puma population has been decreasing for the past few years. but NOT Hari Seldon says that the Empire is decreasing.

A crucial difference between decline and decrease in this last case is that decline can be used to indicate a loss of power, influence, significance, etc., whereas decrease can only be used for a reduction in quantity. Thus you can say both The population is decreasing and The population is declining, but while you can say The Empire is declining, you cannot say The Empire is decreasing, since there's still only one Empire.

Answer 2

I think the key fact is that whereas decrease is used to indicate that a quantity is becoming smaller, decline is to point to the worsening of a situation. For example, we can talk about the decline of an empire, but not about the decrease of an empire (it sounds plain weird.)

To summarize, decline and decrease are synonyms when the decrease of the quantity equate to a worsening of a situation. In your example of the customer base decreasing, that is not the situation worsening, but a deliberate decision. If the decrease of the customer base was out of the company control, one could talk about decline.

Answer 3

If you compare the overlapping meanings, you see that

Decrease can mean:
_{without object}

• to diminish or lessen in extent, quantity, strength, power, etc.: During the ten-day march across the desert their supply of water decreased rapidly

_{with object}

• to make less; cause to diminish: to decrease one's work load.

while decline would mean
_{without object}

• to express courteous refusal; refuse: We sent him an invitation but he declined.
• to bend or slant down; slope downward; descend: The hill declines to the lake.
• (of pathways, routes, objects, etc.) to follow a downward course or path: The sun declined in the skies.
• to draw toward the close, as the day.
• to fail in strength, vigor, character, value, etc.; deteriorate.
• to fail or dwindle; sink or fade away: to decline in popularity.
• to descend, as to an unworthy level; stoop.

the dictionary lists also meanings
_{with object}

• to withhold or deny consent to do, enter into or upon, etc.; refuse: He declined to say more about it.
• to express inability or reluctance to accept; refuse with courtesy: to decline an invitation; to decline an offer.
• to cause to slope or incline downward.

however in meaning of the verb when used with an object there is no meaning that directly corresponds to decrease.

From this I am stipulating that a good criteria might be that of if you are trying the replace "decrease" applied to an object that it will not work, but in cases you want to replace use with no object there is an overlap of meanings and it can be possible (I believe you will find this applies to your examples directly).¹

Semantic is still slightly different; while "decrease" designates any opposite of growth (from etymology, de + cresere), "decline" (from de + clinare, "bend downwards"), in closest sense to "decrease", means that there is such a decrease that would resemble a slope (if for example drawn as a graph).

In another words, while "decrease" is completely appropriate to describe either one time or prolonged, unrepresentative or representative, small or large events, "decline" is reserved for a significant event that has some duration (significant does not mean it is appropriate only for empires or whole civilizations, you can talk about decline in the sales of ink, and it suggest that it is more serious, or significant, than just a decrease of sales).

---

¹ Keep in mind that this "rule" is inferred only from meanings in the dictionary.com.

Answer 4

Without an object, they're often interchangeable:

The number of users decreased on its own. = The number of users declined on its own.

With an object, decrease refers to causing a decrease, but unfortunately for your student, decline does not refer to causing a decline: it only refers to refusal.

I decreased the number of users that he proposed. = I lowered it.
I declined the number of users that he proposed. = I refused it.

Answer 5

Coming back to your original question:

Does anyone have a good rule or way of explaining when to use 'decline' vs. 'decrease'?

1) If it is a person or other entity doing the "declining" or "decreasing", the meanings are totally different.

If I "decline my sales over the next quarter" this would be saying (although grammatically odd) that I am refusing sales over the next quarter. This is very different to if I "decrease my sales over the next quarter", which is saying that I am reducing my sales over the next quarter.

In other words, if there is an object after decline (I decline something) then it means refuse instead of reduce. This is why your student's example of "A company needs to decline its customer base" is wrong.

2) If the declining is just happening, it is much closer but still subtly different.

I can say that sales "declined last quarter" or I can say that sales "decreased last quarter". Unlike your student's example, neither of these sentences are now wrong.

However I agree with you that there is a subtle difference here, but probably a difficult one to find in any dictionary.

I personally use "decline" to illustrate something having taken place over a longer term. Indeed as others have pointed out, something can be "in decline" meaning that it continues to be in the state of decline. One person has said "decline" is only for situations worsening, but that's not true - A country's crime rate can be in decline, for example.

Decrease, on the other hand, usually implies more of a one-off incident. Crime rate has decreased compared to last year, for example - but it's been in decline for 30 years.

Answer 6

A good rule would be, that "decline" as a verb, if wanted to mean "decrease", can only be used when there is no objective following the verb

i.e. "The stocks are declining/the stocks are declining steadily("steadily" is not an objective")

Other examples are : "The empire declines", but an addition of an objective changes the meaning of "decline"

"The empire declines the freedom of people".

Only modifiers (adjectives, adverbs, etc.) can be added, and "decline" will remain "decrease" i.e. "The empire declines rapidly".