What is the difference and relation between chanda and cetana?

When a puthujjana man sees a beautiful girl/lady, a passion or love brews in his heart. This motivating 'passion' or 'love' can be compared to 'chanda'.

Similarly, when the inner urge to end suffering manifests or the liberation & joy of The Path is experienced, a similar 'passion' or 'love' manifests. These are 'chanda'.

'Intention' includes making a decision to do something. 'Intention' is more within the sphere of 'thought' where as 'chanda' is more within the sphere of 'emotion'.

I imagine 'chanda' occurs before 'intention'. For example, you feel unhappy about life and something within you moves you to search for a solution. The 'emotion' or 'will to live/will to be happy' within you that moves you is 'chanda'. From this chanda you act to search for a solution. This decision to act is 'intention'.

SN 51.20 is about the Four Iddhipada. Here, 'chandha' occurs 1st and 'intention' ('citta') occurs later.

These four bases of power, when developed & pursued, are of great fruit & great benefit. And how are the four bases of power developed & pursued so as to be of great fruit & great benefit?

1. There is the case where a monk develops the base of power endowed with concentration founded on desire (chando; zeal; enthusiasm)...

2. He develops the base of power endowed with concentration founded on persistence (vīriya; energy)...

3. He develops the base of power endowed with concentration founded on intent (citta; mind; mental development) ...

4. He develops the base of power endowed with concentration founded on discrimination (vīmaṃsā; inquiry; investigation)...

SN 51.20

Remember my answer about the attention/association process?

There I explained how our attention works under the hood as a cyclic association process with feedback. Remember, how the new associations either support or crowd out the current topic?

Cetana is exactly that in-the-moment "incline" in the cyclic association process, in some direction, that shifts it from one topic to another. It is the ability of the new topic to iteratively crowd out the old topic. In other words it is the relatively more attraction the new topic has over the old topic.

For example, if I open my pantry looking for plastic trash bags, and notice a bar of chocolate, then my thinking gets momentarily dominated by the memory of the sensation of chocolate dissolving in my mouth, and despite having an entirely different goal, I suddenly start getting pulled in the direction of taking a bite of the chocolate. That's Cetana. Subjectively I may think, "oh, why don't I take a little bite of that chocolate?" So in one sense you could say "I saw the chocolate and decided to have a piece". In the other sense, we can say it's the chocolate that has attracted you. It is not one or the other, these are just two different perspectives on the same thing.

This switch from trash bag to chocolate does not happen instantaneously. Instead, there's a shift from one to the other, over some short but not insignificant stretch of time. Perhaps a few seconds. You see the chocolate and feel the pull, and while your eyes are still searching for that trash bag, your hands are taking the chocolate bar and your mouth is biting it.

That shift or inclination in your attention is Cetana.

While Chanda is something entirely different. Chanda is when the child saw a puppet in the toy store, and having come home keeps asking mom to buy the puppet. And the mom says, "but what are you gonna do with it, after a day you will just throw it in the box". And the child says, "no I will do all kinds of things with it." -- "But what things?!" asks mom. -- "I don't know" - says the child, "but I want it".

This vague idea that "when I have it, it will be good" is Chanda.

So Cetana is just an ever present normal regular part of how our mind works moment by moment. Our attention always shifts, there's always an incline. While Chanda is a distinct type of ideation, it is thinking about something and endowing it with good qualities, in your imagination.

Perhaps we could translate Cetana as "impulse" and Chanda as "wishful thinking".

OP: What is the difference between chanda and cetana?

Chanda is the desire to act. E.g. if you stand from a seat you have to have the "intention" to do it, but can choose not to if you want

A Comprehensive Manual of Abhidhamma

Cetana is volition. This is what makes you commit a certain course of action to realise a goal or a wish. E.g. I a feeling hungry hence I will to get up and go to the fridge to get some food.

A Comprehensive Manual of Abhidhamma

OP: How do these two relate to each other?

Cetana is what pulls you in a certain direction in taking action. Chanda is the desire to do the act. E.g. (1) I am feeling hungry, but I am lazy to get up from bed. Here I have the intention but not the will to act. (2) I have money to buy a beggar or donate it to a beggar, but I choose to donate it. Here there is an intention to eat and donate but volition to donate.

Chanda is karmically neutral. Cetana is what decides the karma.

OP: If they are related, which one comes first, and which after?

They are present in the same mind moment if Chanda occurs. Cetana is a universal mental factor and is there in every mind moment. Chanda is an occasional factor hence there only in certain mind moments.

OP: Is one a condition for the other?

Cetana is the driving force which conditions chanda also.