At 1:38:30 AM on Saturday, June 27, 2009, Paul David Hansen wrote:

> Actually, the 'th' sound in 'these', 'them', 'those',
> 'think', 'thought' and 'theory' are all the same: 'þ'.

No, they are not the same: <these>, <them>, and <those> have
the voiced fricative, <ð>, and <think>, <thought>, and
<theory> have the voiceless fricative, <þ>.

> The 'ð' sound is the 'th' sound in 'bath' and 'with, etc.

<Bath> has the voiceless fricative, <þ>; it's the verb
<bathe> that has the <ð> sound. <With> can have either:
some speakers consistently use <þ>, so that it rhymes with
<myth>, some consistently use <ð>, and some use both at
different times.

Brian