I am not sure what are the possible part-of-speeches of 只有
What are the part-of-speeches of 只有 in these sentences?
只有 can mean 'only/ just/ merely' in the first example
水深也'只有'十二米 = "The water depth is only/ just/ merely 12M"
'也' before '只有' is a modal word that put emphasis on the 'not substantial' aspect in the term 'only/ just/ merely', if '只有' means 'only', '也只有' would mean 'just only'
只(only) is an adverb for the verb 有 (has) '十二米' here
只有 can only mean 'only' in the second example, because there is a "才有" (can then have) in the second part of the sentence.
'只有'通过学者的社区考验过的思想，才有活力 = "Only through scholars' socially experimented thinking, can then have life (be alive).."
'才有' in the second part indicates the statement in the first part is a requirement'
只有 (only) is an adverb for the verb 通过 (thought) here
(only: Old English ænlic, anlic "only, unique, solitary," literally "one-like,")
'only' describes the depth of the water, (e.g. the depth is unknown, irregular, deceptive, 12 metres) I would set 'only' as an adjective for 12 metres (which is deep for a person, but shallow for a container ship. Implication: the water may not have sufficient depth.), '1 times 12 metres', so only is basically 1 "one-like".
隻 （= 只） shows 1 bird 隹 in the right hand 又 （a picture of the right hand) with a basic meaning of '1 thing'.
As Tang Ho, in my opinion, rightly points out, 只有 ... 才有 seem to hang together, only when .... only then. (Chinese is full of such double constructions.)
Since when and then both indicate times, in this case projected into the future, I would stick with 'only' as an adjective, an adjective for time. (the only time)
The only time the ideas of the academic community flower is when they are put to the test.
The one time the ideas of the academic community flower is when they are put to the test.