I am learning japanese grammar via Tae Kim (http://www.guidetojapanese.org/learn/grammar). I read that to change a u-verb to potential form, replace the -u ending with a -e ending and add -ru. For example 持てる or 待てる to mean can hold or can wait.
The same verb 持つ, when conjugated to its continuous tense becomes 持っている, which is sometimes simplified to 持てる. I feel like this causes ambiguity, for example, ペンは持てる can mean "I am holding a pen" or "I can hold a pen". The question is, how does one distinguish between the 2 meanings, or is there a completely different way to say these things? I read that the topic particle (を) cannot be used with the potential form of verb, so if the sentence changes to ペンを持てる, it would most likely mean "I am holding a pen", but when the particle is は, it is unclear, at least to me