There are three systems of verbs based on the three principal parts, as presented by this text:

In the present system – the first principal part – are three tenses, both active and passive: present, future and imperfect

      dūcit – he leads, he is leading, he does lead

      dūcitur – he is led, he is being led

      dūcet – he will/shall lead

      dūcētur – he will/shall be led

      dūcēbat – he used to lead, he was leading, he led

      dūcēbātur – he used to be led, he was being led

In the perfect system – the second principal part – are three tenses, in the active voice:

perfect, pluperfect and future perfect

      dūxit – he led, he has led, he did lead

      dūxerat – he had led

      dūxerit – he will have led

In the supine – or perfect passive – system there are these same three tenses in the passive voice:

      ductus est – he was led, he has been led

      ductus erat – he had been led

      ductus erit – he will have been led

The future active participle – along with the future active infinitive (the future active participle plus the infinitive esse) – and the first periphrastic (the future active partciple plus finite forms of esse) – also comes from the supine stem: add –ūr- plus first and second declension adjective endings

      participle: vir ductūrus – the man about to lead

      infinitive: ductūrum, -am, -um esse – to be about to lead

      first periphrastic: Mārcus bonam vītam ductūrus est. – Marcus is going to lead a good life.