birti -bit- gismu

x1 is certain/sure/positive/convinced that x2 is true.

See also jetnu, jinvi, krici, djuno, senpi, sruma.

In notes:

djuno
x1 knows fact(s) x2 (du'u) about subject x3 by epistemology x4.
jetnu
x1 (du'u) is true/truth by standard/epistemology/metaphysics x2.
jinvi
x1 thinks/opines x2 [opinion] (du'u) is true about subject/issue x3 on grounds x4.
krici
x1 believes [regardless of evidence/proof] belief/creed x2 (du'u) is true/assumed about subject x3.
senpi
x1 doubts/is dubious/doubtful/skeptical/questions that x2 (du'u) is true.
sruma
x1 assumes/supposes that x2 (du'u) is true about subject x3; [epistemology].
ju'o
attitudinal modifier: certainty - uncertainty - impossibility.
bitybi'o
x1=bin1=bir1 becomes certain that x2=bir2 under conditions x3=bin3.
bitygau
g1 convinces/persuades b1 that b2 is true.
ciplanli
l1 experiments l2=c2 by means l3.
selbirti
x2=b1 is certain/sure/positive/convinced that x1=b2 is true.