Three consonants carry one idea: holding something in the mind as plausible. From it grow the verb to opine, the causative to explain (make another mind hold it too), the adjective reasonable, the noun for a conjecture, and the abstract for probability. The same root even surfaces in sever panim, a welcoming countenance, the face that makes you feel understood. Pour the letters into different moulds and the whole landscape of thinking, judging and clarifying opens. Every word here is verified against pealim, niqqud included.
The same root runs through the verb system. Each binyan is a voice: it bends the one idea into active, passive, causative or reciprocal. Tap to hear.
The plain pa'al "to opine" is literary today; the everyday verb is the causative hif'il "to explain", which is exactly "to cause another mind to hold the thought". The hitpa'el surfaces only in the noun הִסְתַּבְּרוּת (probability) below, where the ת of the hitpa'el slides next to the ס. Pu'al and huf'al are not lexicalized for this root.
Same root letters, different noun moulds (mishkalim). The mould tells you the function: who does it, the act of doing it, or the thing produced.
Strip the prefixes, suffixes and vowels. Three consonants remain, and the meaning lives there.