We all know that the 'th' sound (as pronounced in English, Welsh, Greek srl) doesn't exist in Irish and when it does occur, it's always pronounced as an 'h'. Why is it then that when certain family or placenames are 'transcribed' into English, they are pronounced with a 'th' sound? It's something I've never been able to understand. For example - Enniscorthy, Carthy, Rathmines srl.

I think there may be a combination of factors at play. Remember, it was the English who Anglicized Irish place names, and in most cases they were not themselves Irish speakers (and, as has been the English practice all over the world, they really couldn't be bothered to listen closely to, and emulate, native speakers of the language). In some cases, the English saw the Irish word and wrote it down accurately but put an English pronunciation on it (for example, pronouncing "rath" as "wrath"). In other cases, they heard the typical Irish broad "t," which sounds "foreign" to English, and modified it to an English "th" (or, in some cases, to an English "t," depending on who was doing the talking and who was doing the listening).

Redwolf

The interesting thing is that th was originally pronounced /θ/ in Old Irish, as in Welsh, etc.

So even though the modern Irish pronunciation of the name Eithne is /eN´ə/ EN-yeh "Enya", the pronunciation /eθNə/ ETH-nuh is at the same time an "anglicization" _and_ an older Irish pronunciation of the name.

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Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

As Breandán said "th" existed in Classical Irish. Both its voiced version found in the English "this", written in Classical
Irish as dh and the unvoiced version found in English "thin", written as th in Classical Irish.

Bliain had the older spelling Bliadhain for example, because it used to be pronounced with a th sound in the middle.
You have to remember things like this or otherwise Bardic poems don't sound right when you read them, i.e. if you use modern Irish pronunciation they don't rhyme.

Although I think the "th"-sounds stopped being used in everyday Irish (i.e. anybody who wasn't a Bard) in about the 13th century.
For that reason I'd say Redwolf has the right explanation about the place names.

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The dialect I use is Cork Irish.
Ar sgáth a chéile a mhairid na daoine, lag agus láidir, uasal is íseal

Eithne - this maybe Enya in some dialects, but the pronunciation in Munster Irish is not clear to me. Could it be /ehin'i/?

I'm not sure how many "English" people have been involved in drawing up English versions of Irish placenames - I would say probably none. Most of these versions of Irish placenames arose naturally - there wasn't a "Commission of Placenames" set up in the 14th century to devise names.

The Anglo-Irish were probably the ones who played the largest role in generating (naturally) the placenames. The more minor a placename was, the more unlikely it becomes that anyone outside a certain locality had heard of it - the local gentry would know it and would have had a name for it, but no one English knew anything about Enniscorthy et al. Go back to a certain point and history, and most of the gentry had to be functional in Irish, particular outside Leinster.

The ancestors of the modern Irish nation include: Gaels, Vikings (who founded all of the older cities), Normans, Anglo-Irish of English, Scottish and Welsh origin.

Yes, that's more accurate. Most English placenames were generated naturally as the population switched from Irish to Hiberno-English.

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The dialect I use is Cork Irish.
Ar sgáth a chéile a mhairid na daoine, lag agus láidir, uasal is íseal

Go raibh maith agaibh go léir
(the next question is why do family names such as O'Flaherty, O'Rafferty and Reilly end with a 'y' sound in English?)

Some of these names were anglicised differently in different parts of Ireland - like Twohey, Twohig - as Tuathaigh is pronounced differently in different Irish dialects.

Another thing to remember is that family names and place names in any language often resist changes in the language and retain older pronunciations long after the language itself has moved on.

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Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

Names like 'Ó Raghallaigh', would they not have come from personal names like 'Raghallach' and so the ending 'í' be natual? With names ending in 'e', perhaps it was pronounced like an i in some areas?

And as for the dental fricatives, would you say there were 4 of them or is that just my imagination due to the caol le caol rule?

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