What, if any, is the difference between โต and ใหญ่? I know ใหญ่ means "big, large" and โต means "big, large or grown up". I assume โต can only be used to refer to a person who has grown up, but are there any other differences?

Can the two words be used interchangeably in all other situations?

Thanks!

โต normally be used to tell something that has grown up such as ต้นไม้ต้นนี้โตไว, ฉันโตขึ้นฉันจะเป็นหมอ, ลูกไก่ตัวนั้นตัวโต

An interesting observation is that โต is also a verb, เจริญขึ้น. I guess that means that you are showing a condition when you use โต and a relative quality when you use ใหญ่. ต้นไม้ใหญ่ means relative to other trees. ตนไม้โต would mean that the tree is fully developed. เติบโต เติบใหญ่ are interchangeable and would seem to contradict this theory but they are compound words.

I would be interested in testing this difference between verbs and adjectives/adverbs taking other examples to see how my theory holds up.

Edit: I forgot of course that โต is also used as a วิเศษณ์ in which role I guess they must be interchangeable, but I can't bring myself to say บ้านโต! I think that in this role it is confined to the adverb role, คุยโต อวดโต วางโต are the three examples in my RID.

บ้านใหญ่โต = บ้านหลังนี้ใหญ่โตดี

คุยโตโอ้อวด = นายคนนั้นชอบคุยโตโอ้อวด

อวดใหญ่อวดโต = เค้าชอบอวดใหญ่อวดโตประจำ

วางใหญ่วางโต = กำนันชอบทำตัววางใหญ่วางโต

คนใหญ่คนโต = เธอชอบทำตัวเหมือนกับคนใหญ่คนโต

as the example but I still do know how the exactly rule to use them. And the major differences are as tgeezer said.

Sorry for the late reply to this, just read it.

I am no expert on the Thai language, but IMHO these are two seperate words that are not inter- changeable.

Reason for saying so, next time you are in a barbers check out the price list written it Thai, it usually goes something like this,

เด็กเล็ก

เด็กใหญ่

เด็กโต

The prices are usually something like, 20 baht, 30 baht and 40 baht.

The way it was explained to me was, dek lek child 12 years or younger, dek yai, teenager less than 16, dek to, teenager 16-19 years old.

So while they are both, เด็กวัยรุ่น its an indicator of the age group/range.

ใหญ่ is to describe the body or shape, or factual

โต is use most likely with abstract

but exactly the same meaning, sometimes we use those two words together ใหญ่โต = BIG

Your house is very big = บ้านของเธอใหญ่โตมาก

Your body is so big = คุณตัวใหญ่จัง, คุณตัวโตจัง

meanwhile, we don't use โต separate with ใหญ่ to describe the house(บ้าน) or many objects

บ้านคุณโตจัง = Failed

บ้านคุณใหญ่จัง = YES