Voiced and Unvoiced TH

[cris_toni]

Greetings!

How can I know if a word is voiced or unvoiced TH?Is there any rules regarding this? Thank you!

[banderas]

Originally Posted by cris_toni

Greetings!

How can I know if a word is voiced or unvoiced TH?Is there any rules regarding this? Thank you!

I think there is no fixed rule. You need to check it in a dictionary.
Check this one:
English Pronouncing Dictionary with Instant Sound Free Online

I feel the unvoiced TH is used mainly before consonants, and the voiced TH is used before vowels.

[ashr]

The sound /θ/ is (unvoiced) as in the word 'thin', whereas the sound/ð/is (voiced)as in the word 'then'. The meaning of 'voiced' or 'unvoiced' sound is dependent on whether there is a vibration in your vocal cords (voiced) or not (unvoiced). Therefore, if you try to put your hand on the front of your neck (over your throat) and try to feel whether your vocal cords are vibrating (as the 'voiced' sound /ð/ in the word 'then') or not ( as the 'unvoiced' sound /θ/ in the word 'thin'), you will be able to decide whether you have pronounced both of them correctly or not.

Another difference between the two sounds is that the sound/θ/, as in the word 'thin', we put the front of the tongue (not the tip of the tongue) between the lower teeth and the upper teeth, whereas the /ð/ sound we put the tip of the tongue (not the front of the tongue) between the lower teeth and the upper teeth. The tongue is divided into 4 positions (tip, front, centre, and back).So if you look carefully to the shapes of the symbols of the two sounds you will recognise that the positions of the tongue in each sound between the lower teeth and the upper teeth are different and consequently you will understand the difference in pronouncing them.

The only similarity between the two sounds is that both of them are called enterdental sounds for that you use both of the lower teeth and the upper teeth in order to pronounce them. Also they are called fricatives for that when it comes to pronouncing them the airsteam is nearly tottal blocked (not completely blocked) in the mouth and it goes smoothly along the center of your tongue to outside of your mouth.